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WSJ'-' 



THE ELEMENTS 



PHYSIOLOGY AND HYGIENE: 



A TEXT-BOOK 



VOR EDUCATIONAL INSTITUTIONS* 



pa- 
thos. H. HUXLEY, LL.D., F.R.*. 

A NO 

WM. JAY YOlJMANS, M.D. 



UXVI8JBD EDITION 

\\ ITU M A N V N K W I I. I T - 1 B ATI- 



1MV^\-C-\ 



NEW rOBK ;• ' IN< INNATI ■:■ CHICAGO 

\ M E RIC A \ B 5 COW I" A \ S 






Copyright, 1863 and 1S73, by D. APPLETON & CO. 
Copyright, 1896, by WM. JAY YOUMANS. 



/ 



in 



PEEFACE 

TO THE REVISED EDITION. 



In the preface to the first American eartion of this 
work, published in 1867, its joint authorship was thus ex- 
plained : u My friend and teacher, Professor Huxley, having 
been for a considerable time engaged in the preparation of 
an elementary work on Physiology, at such brief intervals 
as he could snatch from his laborious scientific researches, 
and it having been suggested to him that its republication 
in this country might be desirable, he confided the early 
sheets of the work to me, to make such additions of matter 
and modifications of form as might be thought proper to 
adapt it to the circumstances and requirements of Ameri- 
can education." I accordingly revised the form, without 
disturbing Professor Huxley's text, and added several 
chapters on Practical Hygiene. 

The author's aim in the preparation of the volume was 
explained in the following passages : 

M My object in writing it lias been to set down, in plain 
and concise language, that which any person who desires 
to become acquainted with the principles of Human Physi- 



4 PREFACE. 

ology may learn, with a fair prospect of having but little 
to unlearn as our knowledge widens. 

" It is only by inadvertence, or from an error in judg- 
ment, therefore, that the work contains any statement, or 
doctrine, which cannot be regarded as the common prop- 
erty of all physiologists. I have endeavored simply to 
play the part of a sieve, and to separate the well-estab- 
lished and the essential from the doubtful and the unim- 
portant portions of the vast mass of knowledge and opinion 
we call Human Physiology." 

Professor Huxley's work has been thoroughly tested. 
It has gone through many impressions in England, has 
been translated into several of the Continental languages, 
has been extensively used in this country ; and the general 
verdict of men of science, and of eminent educators, has 
been that it is the most valuable and authentic digest of 
the elementary facts and principles of Physiology that 
is anywhere to be found. 

There was, nevertheless, one fault in the first edition 
of Professor Huxley's book, which grew out of the fact 
that he was a man of conscience as well as a man of sci- 
ence, and recognized a duty to the subject he was treating. 
Offended by that looseness of style and inaccurate repre- 
sentation which mark the popular manuals of the subject, 
and feeling that there can be no real educational benefit 
in scientific study without mental exertion, he wrote with 
a conciseness and a compression w T hich made parts of his 
book too difficult for average pupils. The present edition 
has, therefore, been carefully revised and much of it re- 
written with more fullness of illustration and simplicity 
of statement ; while familiar words have been substituted 



PREFACE. 5 

for technical terms as far as is consistent with precision. 
Professor Huxley stands high as a master of pointed and 
forcible English, and, in this respect, his volume may now 
be offered as without rival among the books of its class. 

A large number of new engravings have been intro- 
duced into the volume, and a chapter has been added on 
the M Physiological Constants," that will be of value to 
the student in recapitulating and combining the general 
results of the science. That the dimensions of the book 
might not be increased, the first chapter of the former edi- 
tion has been omitted, together with the section on the 
forms of mental impairment. Some important additions 
have, however, been made to the chapter on "Air and 
Health." 

The eminent claim of Professor Huxley's " Elementary 
Physiology" is, that, while up to the times, it is trust- 
worthy in its presentation of the subject ; while rejecting 
discredited doctrines and doubtful speculations, it embodies 
the latest results that are established, and represents the 
present actual state of physiological knowledge. 

Probably, the most important advance which has been 
lately made in the field cf science consists in the establish- 
ment of the great principle of the correlation and conser- 
vation of forces. Accordingly, regarding Physiology as 
strictly the science of vital actions or living forces, Pro- 
SOT Huxley tacitly conforms the whole plan of his work 
to this fundamental principle. Committing himself to no 
unsettled theories respecting the transformations of en- 
ergy, he nevertheless Hews the living organism dynami- 
cally^ a- a problem of the disturbance 1 and restoration of 
equilibrium between the receipt and expenditure of matter 



6 PREFACE. 

and force. The functions of alimentation, circulation, res* 
piration, and secretion, and the exercise of physical and 
mental power, are considered in the light of losses and 
gains to the system, and with constant reference to the 
physiological balance of forces. 

My own additions to the volume have been made in 
response to a growing demand that the subject of Hygiene, 
in both its bodily and mental aspects, shall receive increas- 
ing attention in general education. I trust that the ac- 
knowledged importance of this subject, as well as the ad- 
vantage of dealing with it separately, after the Physiology 
has been mastered, will in some degree promote the favor- 
able reception of the work by the teachers of the country. 

W. J. Y. 

New York, August, 1873. 



COXTEXTS. 



PART I. 

ELEMENTARY PHYSIOLOGY. 



CHAPTER L 

PAGE 

a (texeral View of tiie Structure and Functions of the 

Human Body 11 

E t. 1.— The Bodily Actions 11 

2.— Work and Waste 12 

3.— Outlines of the Bodily Structure ... 16 

4.— The Bodily Tissues 19 

5. — The Combination of Actions .... 23 

6. — Nutrition, Circulation, Excretion .... 26 

7. — Lite and Death 30 

CHAFTEB II. 

The Vascular Bysrii and tiie Circulation 34 

- * t. 1. — The Vascular System ..... 34 

2. — Connections and Structure of the Heart 42 

3. — Working of the Heart and Vessels . 

4.— The General Circulation 55 

CHAPTER III. 

Tnp Bloop and td:e Lymph 7* 

l. — The Microscopical Qementfl of the Blood . . 78 

2. — IVoj the Blood 81 



8 CONTENTS. 

CHAPTER IV. 

PAGE 

Respiration 91 

Sect. 1. — Arterial and Venous Blood .... 91 

2. — The Lungs and their Office 96 

3. — The Respiratory Mechanism .... 102 

4. — Inspiration and Expiration . . . . 108 

5. — Effects of Respiration 114 

CHAPTER V. 

The Sources op Loss and of Gain to the Blood . . . .121 

Sect. 1. — Sources of Loss to the Blood . . . . 121 

2.— Losses and Gains by the Liver . . . .139 

3. — Sources of Gain to the Blood .... 145 

CHAPTER VI. 

The Function op Alimentation 156 

Sect. 1. — Properties of Food-S tuffs 156 

2. — Preliminaries of Digestion 163 

3. — Stomach-Digestion 169 

4. — Intestinal Digestion 174 

CHAPTER VII. 

Motion and Locomotion 181 

Sect. 1. — Instruments of Motion . . • . . . .181 

2. — Mechanism of Bodily Movement . . . 187 

3. — Movements of Locomotion . 202 

4. — Vocal Movements 204 

CHAPTER VIII. 

Sensations and Sensory Organs 214- 

Sect. 1. — Reflex Action — Groups of Sensations . . 214 

2.— Touch, Taste, and Smell 218 

3. — The Mechanism of Hearing .... 226 
4. — Working of the Auditory Mechanism . . .238 

CHAPTER IX. 

The Organ of Sight 243 

Sect. 1. — Structure and Action of the Retina . . .243 

2.— The Luminous Agent 254 

3. — The Intermediate Apparatus 256 
4. — Focal Adjustment 



260 



5. — Appendages of the Eyeball 264 



CONTEXTS. 
CHAPTER X. 

PAGE 

Sensations and Judgment 26? 

Sect. 1. — Compound Sensations 26? 

2. — Delusions of Judgment ..... -70 

3. — Visual Sensations and Mental States . . . 278 

CHAPTER XI. 

The Nervous System and Innervation 2S6 

- r. 1.— The Spinal Cord— Reflex Actions . . 286 

■J.— The Brain 299 

3.— The Cerebral Nerves 3<>4 

4. — Unconscious Cerebration 3<>S 

CHAPTER XII. 

Histology : or, the Minute Structure of the Tissues . . . 313 

Sect. 1. — Dermal Tissues 313 

2.— Interior Tissue^ 320 

S. — Osseous Tissues 326 

4. — Muscular and Nervous Tissues .... 333 

CHAPTER XIII. 

Anatomical and Physiological Constants .... 339 



PART II. 

ELEMENTARY U Yd I EXE. 



CHAPTER XIV. 
and Aim- of Hygiene 344 

CHAPTER XV. 

Air and Health :::,ii 

- .. l. — Composition and Office of the Air . . . 350 

2. — [mporities of the Air 

-Morbid Effects Of Impure Air .... :>r>s 

i. — Purification of the Air ..... 364 



10 CONTENTS. 

CHAPTER XVI. 

PAGE 

Water and Health 370 

Sect. 1. — Physiological Offices of Water . . . . 370 

2.— Different Kinds of Water 371 

3.— Morbid Effects of Impure Water ... 378 

4. — Purification of Water 381 

CHAPTER XVII. 

Food and Health . . . . 383 

Sect. 1. — The Alimentary Principles of Food . . . 383 

2.— Animal Foods 386 

3.— Vegetable Food . . . ... .390 

4. — Auxiliary Foods 394 

5. — Culinary Preparation of Foods . . . .399 

6.— Injurious Effects of Bad Diet .... 402 

CHAPTER XVIII. 

Clothing and Health 410 

Sect. 1. — Properties of Clothing Material . . . 410 
2. — Manner of dressing the Body . . . .413 

CHAPTER XIX. 

Exercise and Health 420 

Sect. 1. — Labor and Exercise 420 

2.— Effects of Regulated Exercise .... 421 

3. — Excessive and Insufficient Exercise . . . 425 

CHAPTER XX. 

Mental Hygiene 429 

Sect. 1. — Relations of Mind and Body .... 429 

2. — Causes of Mental Impairment . . . . 432 




Am 



EXPLANATION OF THE PLATE. 
Figr. I.— The Human Skeleton in Profile. 



In the Skull. 



Xa. The Nasal bones. 
Fr. The Frontal bone. 
Pa. The Parietal bones. 
Oc. The Occipital bono. 
Mk. The Mandible or Lower i 

Jaw. 
«Sf. The Sternum. 
P. The Kibs. 
P . The Cartilages of the [ 

Kibs. 
8. The Sacrum. 
CfaL The Coccyx. 

Sep. The Scapula, or Shoulder-Blade. 
(7. The Clavicle, or Collar- Bone. 
//. The Humerus. ^ 

Ra. The Radius. 
T. The Ulna. 
(p. The Carpus. 



Me. 
D. 



In the 
Thorax. 



- In the Arm. 



i the Arm. 



The Metacarpus. "] 

The Phalanges of the I T 
Fingers or Digits ( 1D 
of the Hand. J 

i, ii, in, iv, v. The Thumb, or Pollex, and 
the succeeding Fingers. 



) Whic] 

V the] 

. ) Os i] 



11. The Ilium, 

Pb. The Pubis, 

Is. The Ischium 

F. The Femur. 

Tb. The Tibia. 

Fb. The Fibula. 

T. The Tarsus. 
j 3ft. The Metatarsus. 
i D. The Phalanges of the 
Toes, or Digits of the | 
Foot. 



hich together form 
Haunch-bone, or 
innominatum. 



■■ In the Leg. 



Fig*. II —Longitudinal and Vertical Section of the Skull. 

The section passes a little to the left of the middle line. The letters as before, except: 
Eth. The Ethmoid bone. B.O. Part of the Occipital bone. 

To. The Vomer. O.F. The Occipital Foramen. 

The branching lines are the impressions left by the arteries of the membranes of 

the brain upon the inner surface of the wall of the cavity, which lodges the cerebrum. 

Fig. HI.— The Rigrht Scapula. 

An. Acromion process. Gl. Glenoidal cavity. 



Fig-. IV. The Dorsal Aspect of the Bones of the Carpus of the 

Left Hand. 



Sc. Scaphoides. 
Tpm. Trapezium. 
L. Semilunare. 



Tpz. Trapezoides. 
Cu. Cuneiforme. 
M. Magnum. 



P8. Pisiforme. 
Un. Unci forme. 



Figr. V. 

A front view of the Sternum. St.. with the Cartilages of the Ribs, R', and part of the 
Ribs themselves, R. 

Fig. VI.— A Front View of the Pelvis. 

Sm. The Sacrum. Am. The Acetabulum. 7/., Pb., /«., as before. 



Fig. VII.— The Dorsal Aspect of the Tarsus cf the Left Foot. 



Cm Cblctneum. 

An. A-tr;:_- 
-V. Navi< , 



01, ( 9 0». The three Cuneiform bones. 
Ob. The Cuboid. 



PART I. 

ELEMENTARY PHYSIOLOGY. 



CHAPTER I. 

A GENERAL VIEW OF THE STRUCTURE AND FUNCTIONS OF 
THE HUMAN BODY. 

Section I. — The Bodily Actions. 

1. How Bodily Actions are Studied. — The body of a liv- 
ing man performs a great diversity of actions, some of 
which are quite obvious ; others require more or less care- 
ful observation ; and yet others can be detected only by 
the employment of the most delicate appliances of science. 

Thus, some part of the body of a living man is plainly 
always in motion. Even in sleep, when the limbs, head, 
and eyelids may be still, the incessant rise and fall of the 

»t continue to remind us thai we are viewing slumber 
and not death. 

More careful observation, however, is needed to detect 
the motion of the heart j or the pulsation of the arteries; 
or the changes in the size of the pupil of the eye with vary- 
ing light; or to ascertain that the air which is breathed 
out of the body is hotter and damper than the air which is 
taken in by breathing, 



12 ELEMENTARY PHYSIOLOGY. 

And lastly, when we try to ascertain what happens in 
the eye when that organ is adjusted to different distances : 
or what in a nerve when it is excited : or of what materials 
flesh and blood are made : or in virtue of what mechanism 
it is that a sudden pain makes one start — we have to call 
into operation all the methods of inductive and deductive 
logic; all the resources of physics and chemistry ; and all 
the delicacies of the art of experiment. 

2. Scope of Human Physiology. — The sum of the facts 
and generalizations at which we arrive by these various 
modes of inquiry, be they simple or be they refined, con- 
cerning the actions of the body and the manner in which 
those actions are brought about, constitutes the science of 
Human Physiology. An elementary outline of this science, 
and of so much anatomy as is incidentally necessary, is the 
subject of the following chapters ; of which I shall devote 
the present to an account of so much of the structure and 
such of the actions (or, as they are technically called, 
" functions ") of the body, as can be ascertained by easy 
observation ; or might be so ascertained if the bodies of 
men were as easily procured, examined, and subjected to 
experiment, as those of animals. 

Section II. — Work and Waste. 

3. Bodily Loss or Expenditure. — Suppose a chamber, 
with walls of ice, through which a current of pure ice-cold 
air passes ; the walls of the chamber will of course remain 
unmelted. 

Now, having weighed a healthy living man with great 
care, let him walk up and down the chamber for an hour. 
In doing this he will obviously exercise a great amount of 
mechanical force ; as much, at least, as would be required 
to lift his weight as high and as often as he has raised 
himself at every step. But, in addition, a certain quantity 
of the ice will be melted, or converted into water ; show- 
ing that the man has given off heat in abundance. Fur- 



WORK AND WASTE. 13 

thermore, if the air which enters the chamber be made to 
pass through lime-water, it will cause no cloudy white pre- 
cipitate of carbonate of lime, because the quantity of car- 
bonic acid in ordinary air is so small as to be inappreciable 
in this way. But if the air which passes out is made to 
take the same course, the lime-water will soon become 
milky, from the precipitation of carbonate of lime, showing 
the presence of carbonic acid, which, like the heat, is given 
off by the man. 

Again, even if the air be quite dry as it enters the cham- 
ber (and the chamber be lined with some material so as to 
shut out all vapor from the melting ice-walls), that which 
is breathed out of the man, and that which is given off 
from his skin, will exhibit clouds of vapor; which vapor, 
therefore, is derived from the body. 

After the expiration of the hour during which the ex- 
periment has lasted, let the man be released and w r eighed 
once more. He will be found to have lost weight. 

Thus a living, active, man constantly exerts mechanical 
for>t % gives off heat, evolves carbonic add and loafer, and 
undergoes a loss of suhstance. 

4. A Physiological Income indispensable. — Plainly, this 
state of things could not continue for an unlimited period, 
or the man would dwindle to nothing. But long before 
the effects of this gradual diminution of substance become 
apparent to a bv-stander, they are felt by the subject of the 
experiment in the form of the two imperious sensations 
called hunger and thirst. To still these cravings, to restore 
the weight of tin 1 body to its former amount, to enable it 
to continue giving out heat, water, and carbonic acid, at 
the . for an indefinite period, it is absolutely nec- 

iry that the body should be supplied with each of three 
things, and with three only. These are, firstly, fresh air; 

>ndly, drink — consisting of water in some shape or 
other, however much it may be adulterated; thirdly, food. 
That compound known to chemists as proteid matter, and 



14 ELEMENTARY PHYSIOLOGY. 

which contains carbon, hydrogen, oxygen, and nitrogen, 
must form a part of this food, if it is to sustain life in- 
definitely ; and fatty, starchy, or saccharine matters ought 
to be contained in the food, if it is to sustain life con- 
veniently. 

5. Forms of Excretions. — A certain proportion of the 
matter taken in as food either cannot be, or at any rate, is 
not, used ; and leaves the body, as excrementiiious matter, 
having simply passed through the alimentary canal without 
undergoing much change, and without ever being incorpo- 
rated with the actual substance of the body. But, under 
healthy conditions, and when only so much food as is neces- 
sary is taken, no important proportion of either proteid mat- 
ter, or fat, or starchy or saccharine food, passes out of the 
body as such. Almost all real food leaves the body in the 
form either of water, or of carbonic acid, or of a third sub- 
stance called urea, or of certain saline compounds. 

6. Absorption of Oxygen. — Chemists have determined 
that these products which are thrown out of the body and 
are called excretions, contain, if taken altogether, far more 
oxygen than the food and water taken into the body. 
Now, the only possible source whence the body can obtain 
oxygen, except from food and water, is the air which sur- 
rounds it. 1 And careful investigation of the air which leaves 
the chamber in the imaginary experiment described above 
would show, not only that it has gained carbonic acid from 
the man, but that it has lost oxygen in equal or rather 
greater amount to him. 

7. Variation of the Physiological Balance.— Thus, if a 
man is neither gaining nor losing weight, the sum of the 
weights of all the substances above enumerated which 
leave the body, ought to be exactly equal to the weight of 
the food and water which enter it, together with that of 

1 Fresh country air contains in every 100 parts nearly 21 of oxygen and 79 of nitro- 
gen gas, together with a small fraction of a part of carbonic acid, a minute uncertain 
proportion of ammonia, and a variable quantity of watery vapor. (See 103.) 



WORK AND WASTE. 15 

the oxygen which it absorbs from the air. And this is 
proved to be the case. 

Hence it follows that a man in health, and "neither 
gaining nor losing flesh," is iricessatltly oxidating and 
wasting away, and periodically making good the loss. So 
that if, in his average condition, he could be confined in 
the scale-pan of a delicate spring balance, like that used 
for weighing letters, the scale-pan would descend at every 
meal, and ascend in the intervals, oscillating to equal dis- 
tances on each side of the average position, which would 
never be maintained for longer than a few minutes. There 
La, therefore, no such thing as a stationary condition of the 
weight of the body, and what we call such is simply a con- 
dition of variation within narrow limits — a condition in 
which the gains and losses of the numerous daily transac- 
tions of the economy balance one another. 

8. Conditions of this Balance. — Suppose this diuraally- 
balanced physiological state to be reached, it can be main- 
tained only so long as the quantity of the mechanical work 
done, and of heat, or other force evolved, remains absolutely 
unchanged. 

Let such a physiologically-balanced man lift a heavy 
body from the ground, and the loss of weight which he 
would have undergone without that exertion will be im- 
mediately increased by a definite amount, which cannot be 
made good unless a proportionate amount of extra food be 
supplied to him. Let the temperature of the air fall, and 
the same result will occur, if his body remains as warm as 
before. 

On the other hand, diminish his exertion and lower his 
production of heat, and either he"w T ill gain weight, or some 
of his food will remain unused. 

9. Equation of Food and Force. — Thus, in a properly- 
nourished man, a stream of fond is constantly entering the 
body in the shape of complex compounds containing com- 
paratively little ; as constantly, the elements of the 



16 ELEMENTARY PHYSIOLOGY. 

food (whether before or after they have formed part of the 
living substance) are leaving the body, combined with 
more oxygen. And the incessant breaking down and oxi- 
dation of the complex compounds which enter the body are 
definitely proportioned to the amount of force the body 
exerts, whether in the shape of heat or otherwise ; just in 
the same way as the amount of work to be got out of a 
steam-engine, and the amount of heat it and its furnace 
give off, bear a strict proportion to its consumption of fuel. 

Section III. — Outlines of the Bodily Structure. 

10. Structure of the Vital Mechanism. — From these gen- 
eral considerations regarding the nature of life, considered 
as physiological work, we may turn for the purpose of tak- 
ing a like broad survey of the apparatus which does the 
work. We have seen the general performance of the en- 
gine, we may now look at its build. 

The human body is obviously separable into head, trunk, 
and limbs. In the head, the brain-case or skull is distin- 
guishable from the face. The trunk is naturally divided 
into the chest or thorax, and the belly or abdomen. Of 
the limbs there are two pairs — the upper, or arms, and the 
lower, or legs ; and legs and arms again are subdivided by 
their joints into parts which obviously exhibit a rough cor- 
respondence — thigh and upper arm, leg and forearm, ankle 
and vjrist, fingers and toes, plainly answering to one an- 
other. And £he two last, in fact, are so similar that they 
receive the same name of digits / while the several joints 
of the fingers and toes have the common denomination of 
phalanges. 

The whole body thus composed (without the viscera) 
is seen to be bilaterally symmetrical ; that is to say, if it 
were split lengthways by a great knife, which should be 
made to pass along the middle line of both the dorsal and 
ventral (or back and front) aspects, the two halves would 
almost exactly resemble one another. 



OUTLIXES OF THE BODILY STRUCTURE. 17 

11. The Vertebral Column. — One-half of the body, di- 
vided in the manner described (Fig. 1), would exhibit, in 
the trunk, the cut feces of thirty-three bones, joined to- 
gether bv a very strong and tough substance into a long 
column, which lies much nearer the d<>rs<d (or back) than 
the ventral (or front) aspect of the body. The bones thus 
cut through are called the bodies of the vertebra?. They 
separate a Long, narrow canal, called the Spinal canal, 
which is placed upon their dorsal side, from the spacious 
chamber of the chest and abdomen, which lies upon their 
ventral side. There is no direct communication between 
the dorsal canal and the ventral cavity. 

12. Internal Organs. — The spinal canal contains a long 
white cord — the spinal cord — which is an important part 
of the nervous system. The ventral chamber is divided 
into the two subordinate cavities of the thorax and abdo- 
men by a remarkable, partly fleshy and partly membranous, 
partition, the diaphragm (Fig. 1, D), which is concave 
toward the abdomen, and convex toward the thorax. The 
alimentary canal (Fig. 1, At.), traverses these cavities 
from one end to the other, piercing the diaphragm. So 
does a long double series of distinct masses of nervous sub- 
stance, which are called ganglia, are connected together 
by nervous cords, and constitute the so-called sympathetic 
(Fig. 1, Sy.). The abdomen contains, in addition to these 
parts, the two kidneys, one placed against each side of the 
vertebral column, the liver, the p>ancreas or "sweetbread," 
and the spleen. The thorax incloses, besides its segment 
of the- alimentary canal and of the sympathetic, the heart 
and the two lungs. The latter are placed one on each 
Bide of tin- heart, which lies nearly in the middle of the 
thorax. 

13. The Head and Brain. — Where the body is succeeded 
by the head, tin- uppermost of the thirty-three vertebral 
bodies is followed by a continuous mass of bone, which ex- 
tends thrdUgh the whole length of the head, and, like the 



18 



ELEMENTARY PHYSIOLOGY. 



spinal column, separates a dorsal chamber from a ventral 
one. The dorsal chamber, or cavity of the skull r , opens 
into the spinal canal. It contains a mass of nervous matter 
called the brain, which is continuous with the spinal cord, 
the brain and the spinal cord together constituting what is 
termed the cerebrospinal axis (Fig. 1, C.S., C.3.). The 




Fig. 3. 



Fig. 1. 



Fig. 1.— A diagrammatic section of the human body taken vertically through the 
median plane. O.S., the cerebro-spinal nervous system; .#"., the cavity of the nose; 
M., that of the mouth ; Al. Al., the alimentary canal represented as a simple straight 
tube; H., the heart; D., the diaphragm; Sy., the sympathetic ganglia. 

Fig. 2.—A transverse vertical section of the head taken along the line a &, Fig. 1 ; 
letters as before. 

Fig. 3.— A transverse section taken along the line c cl, Fig. 1 ; letters as before. 



THE BODILY TISSUES. 19 

ventral chamber, or cavity of the face, is almost entirely 
occupied by the mouth and pharynx, into which last the 
upper end of the alimentary canal (called gullet or oesopha- 
gus) opens. 

14. The Human Body a Double Tube. — Thus, the study 
of a longitudinal section shows US that the human body is 
a double tube, the two tubes being completely separated 
by the spinal column and the bony axis of the skull, which 
form the floor of the one tube and the roof of the other. 
The dorsal tube contains the cerebrospinal axis; the ven- 
tral, the alimentary canal, the sympathetic nervous system, 
and the heart, besides other organs. 

Transverse sections, taken perpendicularly to the axis 
o( the vertebral column, or to that of the skull, show still 
more clearly that this is the fundamental structure of the 
human body, and that the great apparent difference be- 
tween tin 1 head and the trunk is due to the different size 
of the dorsal cavity relatively to the ventral. In the head 
the former cavity is very large in proportion to the size of 
the latter (Fig. 2); in the thorax, or abdomen, it is very 
small (Fig. 3). 

The limbs contain no such chambers as are found in the 
body and the head ; but, with the exception of certain 
branching tubes filled with fluid, which are called blood- 
's and lymphatics, are solid or semi-solid throughout. 

Section TV. — The Bodily Tissues. 

15. The Skin. — Such being the general character and 
arrangement of the parts of the human body, it w ill next 
be '.veil to consider into what constituents il may be sepa- 
rated by the aid of no better means of discrimination thai) 

the eye and the anatomist's knife. 

With no more elaborate aids than these, it becomes 

v to separate that tough membrane which invests the 

whole body, and i- called the skin, or integument, from 
the part- which lie beneath it. Furthermore, it i- readily 



20 ELEMENTARY PHYSIOLOGY. 

enough ascertained that this integument consists of two 
portions : a superficial layer, which is constantly being shed 
in the form of powder or scales, composed of minute par- 
ticles of horny matter, and is called the epidermis y and the 
deeper part, the dermis, which is dense and fibrous (Fig. 
40). The epidermis, if wounded, neither gives rise to pain 
nor bleeds. The dermis, under like circumstances, is very 
tender, and bleeds freely. A practical distinction is drawn 
between the two in shaving, in the course of which opera- 
tion the razor ought to cut only epidermic structures ; for 
if it go a shade deeper, it gives rise to pain and bleeding. 

16. Mucous Membranes. — The skin can be readily enough 
removed from all parts of the exterior, but at the margins 
of the apertures of the body it seems to stop, and to be re- 
placed by a layer which is much redder, more sensitive, 
bleeds more readily, and which keeps itself continually 
moist by giving out a more or less tenacious fluid, called 
mucus. Hence, at these apertures, the skin is said to stop, 
and to be replaced by mucous membrane, which lines all 
those interior cavities, such as the alimentary canal, into 
which the apertures open. But, in truth, the skin does not 
really come to an end at these points, but is directly con- 
tinued into the mucous membrane, which last is simply an 
integument of greater delicacy, but consisting fundament- 
ally of the same two layers — a deep, fibrous layer, contain- 
ing blood-vessels and nerves, and a superficial, insensible, 
and bloodless one, now called the epithelium. Thus every 
part of the body might be said to be contained between 
the walls of a double bag, formed by the epidermis, which 
invests the outside of the body, and the epithelium, its con- 
tinuation, which lines the internal cavities. 

17. Connective Tissue. — The dermis, and the deep, san- 
guine layer, which answers to it in the mucous membranes, 
are chiefly made up of a filamentous substance, which yields 
abundant gelatine on being boiled, and is the matter w r hich 
tans when hide is made into leather. This is called areolar. 



THE BODILY TISSUES. 21 

fibrous, or, bettor, connective tissue. 1 The last name is 
the best, because this tissue is the great connecting me- 
dium by which the different parts of the body are held 

together. Thus it passes from tin 4 dermis between all the 
other organs, ensheathing tin 4 muscles, coating tin 4 bones 
and cartilages, and eventually reaching and entering into 
the mucous membranes. And so completely and thoroughly 

does the connective tissue permeate almost all parts of the 
body, that if every other tissue could be dissected away, a 
Complete model of all the organs would be left composed 
oi' this tissue. Connective tissue varies very much in char- 
acter; sometimes being very soft and tender, at others — as 
in the tendons and ligaments, which are almost wholly com- 
posed of it — attaining great strength and density. 

18, The Muscles, — Among the most important of the 
tissues embedded in and ensheathed by the connective 4 tis- 
sue, are some the presence and action of which can -be 
readily determined during life. 

If the upper arm of a man whose arm is stretched out 
be tightly grasped by another person, the latter, as tin 4 
former bends up his forearm, will feel a great soft mass, 
which lies at the fore part of the upper arm, swell, harden, 
and become prominent. As the arm is extended again, tin 4 
swelling and hardness vanish. 

On removing the skin, the body which thus changes its 
configuration is found to be a mass of red flesh, sheathed 
in connective tissue. The sheath is continued at each end 
into a tendon, by which the muscle is attached, on the one 
hand, to the shoulder-bone, and, on the other, to one of the 
bones of the forearm. This mass of flesh is the muscle 

called biceps, and it has the peculiar property of changing 
its dimensions — shortening and becoming thick in propor- 
tion to its decrease in length — when influenced by the will 
a- well as by some other Cau8e8,' and of returning to its 

ry rodi constituent <<f the body, m epidermis, cartilage «>r muscle, Is-eaDed a 
iptar xil.) - MKii oaosci nr<j called stimuli 



22 ELEMENTARY PHYSIOLOGY. 

original form when let alone. This temporary change in 
the dimensions of a muscle, this shortening and becoming 
thick, is spoken of as its contraction. It is by reason of 
this property that muscular tissue becomes the great motor 
agent of the body ; the muscles being so disposed between 
the systems of levers which support the body, that their 
contraction necessitates the motion of one lever upon an- 
other. 

19. The Cartilages and Bones,— These levers form part 
of the system of hard tissues which constitute the skeleton. 
The less hard of these are the cartilages, composed of a 
dense, firm substance, ordinarily known as " gristle." The 
harder are the bones, which are masses either of cartilage, 
or of connective tissue, hardened by being impregnated 
with phosphate and carbonate of lime. They are animal 
tissues which have become, in a manner, naturally petrified ; 
and when the salts of lime are extracted, as they may be, 
by the action of acids, a model of the bone in soft and flexi- 
ble animal matter remains. 

More than two hundred separate bones are ordinarily 
reckoned in the human body, though the actual number of 
distinct bones varies at different periods of life, many bones 
which are separate in youth becoming united together in 
old age. Thus there are originally, as we have seen, thirty- 
three separate bodies of vertebrae in the spinal column, and 
the upper twenty-four of these commonly remain distinct 
throughout life. But the twenty-fifth, twenty-sixth, twenty- 
seventh, twenty-eighth, and twenty-ninth early unite into 
one great bone, called the sacrum / and the four remaining 
vertebras often run into one bony mass called the coccyx. 
In early adult life, the skull contains twenty-two naturally 
separate bones, but in youth the number is much greater, 
and in old age far less. Twenty-four ribs bound the chest 
laterally, twelve on each side, and most of them are con- 
nected by cartilages with the breastbone. In the girdle 
which supports the shoulder, two bones are always dis- 



THE COMBINATION OF ACTIONS. 23 

tinguishable as the scapula and clavicle, The pelvis, to 
which the legs are attached, consists of two separate bones 
called the ossa innominata in the adult; but each os in- 
nominatum is separable into three (called pubis, ischiunft, 

and ilium) in tlu^ young. There arc thirty bones in each 
of the arms, and the same number in each of the legs, 
counting thepatella, or knee-pan. 

All these bones are fastened together by ligaments, or 
by cartilages; and, where they play freely over one an- 
other, a coal of cartilage furnishes the surfaces which come 
into contact. The cartilages which thus form part of a 
joint arc called articular cartilages, and their free surfaces, 
by which they rub against each other, are lined by a deli- 
cate synovial membrane, which secretes a lubricating fluid 
— the synovia. 

Section V. — The Combination of Actions. 

20. How we stand upright. — Though the bones of the 
skeleton are all strongly enough connected together by 
ligaments and cartilages, the joints play so freely, and the 
centre of gravity of the body, when erect, is so high up, 
that it is impossible to make a skeleton or a dead body 
Mipport itself in the upright position. That position, easy 
as it seems, is the result of the contraction of a multitude 
of muscles which oppose and balance one another. Thus, 
the foot affording the surface of support, the muscles of the 
calf (Fig. 4, I) must contract, or the legs and body would 
fall forward. But this action tends to bend the leg; and, 
to neutralize this and keep the leg straight, the great 
muscles in froni of the thigh (Fig. 4, 2), must come into 

play. But these, by the same action, tend to bend the 

body forward on the legs; and, if the body is to be kept 
straight, they musl be neutralized by the action of the 
muscles of the buttocks and of the back ( Fig. 1, III). 

The ered position, then, which we assume so easily 

and without thinking about it, is the result of the combined 



24 



ELEMENTARY PHYSIOLOGY. 



and accurately-proportioned action of a vast number of 
muscles. What is it that makes them work together in 
this way ? 



Fig. 4. 

a diagram illustrating the attachments of some op the most important 
Muscles which keep the Body in the eeect Posture. 

I. The muscles of the calf. II. Those of the back of the thigh. III. Those of the 
spine. These tend to keep the body from falling- forward. 

1. The muscles of the front of the leg. 2. Those of the front of the thigh. 3. Those 
of the front of the abdomen. 4, 5. Those of the front of the neck. These tend to keep 
the body from falling backward. 

The arrows indicate the direction of action of the muscles, the foot being fixed. 

21. Relation of the Mind to the Muscles. — Let any per- 
son in the erect position receive a violent blow on the head, 
and you know what occurs. On the instant he drops pros- 



THE COMBINATION OF ACTIONS L >o 

trate, in a heap, with his limbs relaxed ami powerless. What 
has happened to him? The blow may have been so in- 
flicted as not to touch a single muscle oi' the body; it may 
not cause the loss of a drop of blood: ami, indeed, if the 
u concussion," as it is called, has not been too seven 4 , the 
sufferer, after a few moments oi' unconsciousness, will come 
to himself, and be as well as ever again. Clearly, there- 
fore, no permanent injury has been done to any part of the 
body, least oi all to the muscles, but an influence has been 
exerted upon a something which governs the muscles. And 
this influenee may be the effect of very subtle causes. A 
strong mental emotion, and even a very bad smell, will, in 
some people, produce the same effect as a blow. 

These observations might lead to the conclusion that it 
is the mind which directly governs the muscles, but a little 
further inquiry will show that such is not the case. For 
people have been so stabbed, or shot in the back, as to cut 
the spinal cord, without any considerable injury to other 
parts: and then they have lost the power of standing up- 
right as much as before, though their minds may have re- 
mained perfectly clear. And not only have they lost the 
power of standing upright under these circumstances, but 
they no longer retain any power of either feeling w T hat is 
going on in their legs, or, by an act of their volition, caus- 
ing motion in them. 

22. The Spinal Cord converts Impressions into Move- 
ments. — And yet, though the mind is thus cut off from the 
lower limbs, a controlling and governing power over them 
still remains in the body. For, if the soles of the disabled 

• be tickled, though no sensation will reach the body, 

the legs will be jerked up, just as would bo the case in an 

uninjured person. Again, if a series of galvanic Bhocks be 

r along the spinal cord, the legs will perform movements 

even more powerful than those which the will could pro 
duoe in an uninjured person. And, finally, if the injury is 

Mich a nature that the oord i- crushed or profoundly dis- 



26 ELEMENTARY PHYSIOLOGY. 

organized, all these phenomena cease ; tickling the soles, 
or sending galvanic shocks along the spine, will produce 
no effect upon the legs. 

By examinations of this kind carried still further, we 
arrive at the remarkable result that the brain is the seat 
of all sensation and mental action, and the primary source 
of all voluntary muscular contractions ; while the spinal 
cord is capable of receiving an impression from the exterior, 
and converting it not only into a simple muscular contrac- 
tion, but into a combination of such actions. 

Thus, in general terms, we may say of the cerebrospinal 
nervous centres, that they have the power, when they re- 
ceive certain impressions from without, of giving rise to 
simple or combined muscular contractions. 

23. Special Sensations. — But you will further note that 
these impressions from without are of very different char- 
acters. Any part of the surface of the body may be so 
affected as to give rise to the sensations of contact, or of 
heat or cold; and any or every substance is able, under 
certain circumstances, to produce these sensations. But 
only very few and comparatively small portions of the 
bodily framework are competent to be affected in such a 
manner as to cause the sensations of taste or of smell, of 
sight or of hearing; and only a few substances, or par- 
ticular kinds of vibrations, are able so to affect those re- 
gions. These very limited parts of the body, which put us 
in relation with particular kinds of substances, or forms of 
force, are what are termed sensory organs. There are two 
such organs for sight, two for hearing, two for smell, and 
one, or more strictly speaking two, for taste. 

Section VI. — Nutrition, Circulation, Excretion, 

24, Constant Renewal of Tissues. — And now that we 
have taken this brief view of the structure of the body, of 
the organs which support it, of the organs which move it, 
and of the organs which put it in relation with the surround- 



NUTRITION', CIRCULATION, EXCRETION. 27 

ing world, or, in other words, enable it to move* iii har- 
mony with influences from without, we must consider the 

moans by which all this wonderful apparatus is kepi in 
working order. 

All work, as we have Been, implies waste. The work 
of the nervous system and that of the muscles, therefore, 
implies consumption either of their own substance, or of 
something else. And, as the organism can make nothing, 

it must possess the means of obtaining from without that 
which it wants, and of throwing off from itself thai which 
it wastes ; and we have seen that, in the gross, it docs 
these things. The body feeds, and it excretes. But we 
must now pass from the broad fact to the mechanism by 
which the fact is brought about. The organs which con- 
vert food into nutriment are the organs of alimentation ; 
those which distribute nutriment all over the body are 
organs of circulation ; those which get rid of the waste 
products are organs of excretion. 

25. Alimentary Apparatus. — The organs of alimenta- 
tion are the mouth, pharynx, gullet, stomach, and intes- 
tines, with their appendages. What they do is, first to 
receive and grind the food. They then act upon it with 
chemical agents, of which they possess a store which is re- 
newed as fast as it is wasted ; and in this way separate it 
into a fluid containing nutritious matters in solution or 
suspension, and innutritions dregs or foeces. 

26. Mechanism of Distribution. — A system of minute 
tubes, with very thin walls, termed capillaries, is distrib- 
uted through the whole organism except the epidermis 
and its products, the epithelium, the cartilages, and the 

substance of the teeth. On all sides these tubes pass into 
others, which are called arteries and veins/ while these, 
becoming larger and larger, at length open into the heart, 

an organ which, as we have seen, is placed in the thorax. 
During life, these tubes and the chambers of the heart, 
with which they are Connected, are all full of liquid, which 



28 ELEMENTARY PHYSIOLOGY. 

is, for the most part, that red fluid with which we are all 
familiar as blood. 

The walls of the heart are muscular, and contract 
rhythmically, or at regular intervals. By means of these 
contractions the blood which its cavities contain is driven 
in jets out of these cavities into the arteries, and thence 
into the capillaries, whence it returns by the veins back 
into the heart. 

This is the circulation of the blood. 

27. Exchanges of the Blood. — Now the fluid containing 
the dissolved or suspended nutritive matters which are the 
result of the process of digestion, traverses the very thin 
layer of soft and permeable tissue which separates the cav- 
ity of the alimentary canal from the cavities of the innu- 
merable capillary vessels which lie in the walls of that 
canal, and so enters the blood, with which those capillaries 
are filled. Whirled away by the torrent of the circulation, 
the blood, thus charged with nutritive matter, enters the 
heart, and is thence propelled into the organs of the body. 
To these organs it supplies the nutriment w4th which it is 
charged ; from them it takes their waste products, and, 
finally, returns by the veins, loaded with useless and in- 
jurious excretions, which sooner or later take the form of 
water, carbonic acid, and urea. 

28. Drainage of Waste Matters from the Body. — These 
excretionary matters are separated from the blood by the 
excretory organs, of which there are three — the skin, the 
lungs, and the kidneys. 

Different as these organs may be in appearance, they 
are constructed upon one and the same principle. Each, 
in ultimate analysis, consists of a very thin sheet of tissue, 
like so much delicate blotting-paper, the one face of which 
is free, or lines a cavity in communication with the exte- 
rior of the bod} 7 , while the other is in contact with the 
blood which has to be purified. 

The excreted matters are, as it were, strained from the 



NUTRITION, CIRCULATION". EXCRETION". 29 

blood, through this delicate layer of filtering-tissue, and on 
to its free surface, whence they make their escape. 

Each of these organs is especially concerned in the 

elimination of one of the chief waste products — water, car- 
bonic arid, and urea — though it may at the same time be 
a means of escape for the others. Thus the lungs are 
especially busied in getting rid of carbonic acid, but at the 
same time they give off a good deal of water. The duty 
of the kidneys is to excrete urea (together with other saline 
matters), but at the same time they pass away a large 
quantity of water and a trifling amount of carbonic acid ; 
while the skin gives off much water, some amount of car- 
bonic acid, and a certain quantity of saline matter, among 
which urea is, at all events, sometimes present. 

29. Double Function of the Lungs. — Finally, the lungs 
play a double part, being not merely eliminators of waste, 
or excreta mary. products, but importers into the economy 
of a substance which is not exactly either food or drink, 
but something as important as either — to wit, oxygen. It 
is oxygen which is the great Bweeperofthe economy. In- 
troduced by the blood, into which it is absorbed, into all 
corners of the organism, it seizes upon those organic mole- 
cules which arc disposable, lays hold of their elements, and 

ibines with them into the new and simpler forms, car- 
bonic acid, water, and urea. 

Tiie oxidation, or, in other words, the burning of the-e 
matters, 2'ivos rise to an amount of heat which is as effi- 
cient as a fire to raise the blood to a temperature of about 
100°; and this hot fluid, incessantly renewed in all parte 
of the economy by the torrent of the circulation, warms 
the body, as a house is warmed by a hot-water apparatus. 

30. Regulative Action of the Nerves. — Bui these ali- 
mentary, distributive or circulatory, excretory, and oom- 
bustive pn would be worse than useless it' th< 
were not kept in Btricfl proportion one to another. If the 
state of physiological balance is to be maintained, not only 



30 ELEMENTARY PHYSIOLOGY. 

must the quantity of aliment taken be at least equivalent 
to the quantity of matter excreted ; but that aliment must 
be distributed with due rapidity to the seat of each local 
waste, The circulatory system is the commissariat of the 
physiological army. 

Again, if the body is to be maintained at a tolerably 
even temperature, while that of the air is constantly vary- 
ing, the condition of the hot-water apparatus must be most 
carefully regulated. 

In other words, a combining organ must be added to 
the organs already mentioned, and this is found in the 
nervous system, which not only possesses the function al- 
ready described of enabling us to move our bodies and to 
know what is going on in the external world ; but makes 
us aware of the need of food, enables us to discriminate 
nutritous from innutritious matters, and to exert the mus- 
cular actions needful for seizing, killing, and cooking ; 
guides the hand to the mouth, and governs all the move- 
ments of the jaws and of the alimentary canal. By it, the 
working of the heart is properly adjusted, and the calibres 
of the distributing pipes are regulated, so as indirectly to 
govern the excretory and combustive processes. And these 
are more directly affected by other actions of the nervous 
system. 

Section VII. — Life and Death. 

31. The Vital Actions. — The various functions which 
have been thus briefly indicated constitute tjie greater 
part of what are called the vital actions of the human 
body, and, so long as they are performed, the body is said 
to possess life. The cessation of the performance of these 
functions is what is ordinarily called death. 

But there are really several kinds of death, which may, 
in the first place, be distinguished from one another under 
the two heads of local and of general death. 

32. Local Death. — Local death is going on at every 



LIFE AND DEATH. 31 

moment, and in most, if not in all, parts of the living 
body. Individual cells of the epidermis and of the epithe- 
lium are incessantly dying and being east off, to be re- 
placed by others which are, as constantly, coming into 
separate existence. The like is true of blood-corpuscles, 
and probably of many other elements of the tissues. 

This form of local death is insensible to ourselves, and 
is essential to the due maintenance of life. But, occasion- 
ally, local death occurs on a larger scale, as the result of 
injury, or as the consequence of disease. A burn, for ex- 
ample, may suddenly kill more or less of the skin; or part 
of the tissues of the skin may die, as in the case of the 
slough which lies in the midst of a boil ; or a whole limb 
may die, and exhibit the strange phenomena of mortifica- 
tion. 

The local death of some tissues is followed by their 
regeneration. Not only all the forms of epidermis and 
epithelium, but nerve, connective tissue, bone, and, at any 
rate, some muscles, may be thus reproduced, even on a 
large scale. Cartilage, once destroyed, is said not to be 
restored. 

33. General Death. — General death is of two kinds — 
death of the body as << whole, and death of the tissues. By 
the former term is implied the absolute cessation of the 
functions of the brain, of the circulatory, and of the respira- 
tory organs; by the latter, the entire disappearance of the 
vital actions of the ultimate structural constituents of the 
body. When death takes place, the body, as a whole, dies 
first, the death of the tissues sometimes not occurring until 
after a considerable interval. 

Hence it is that, for son).* little time after what is ordi- 
narily called death, the muscles of an executed criminal may 
be i contract by the application of proper stimuli 

The muscles arc not dead, though the man is. 

34. Modes of Death. — The modes in which death is 
agh< aboui appear at first sight to he extremely varied. 



32 ELEMENTARY PHYSIOLOGY. 

We speak of natural death by old age, or by some of the 
endless forms of disease ; of violent death by starvation, or 
by the innumerable varieties of injury, or poison. But, in 
reality, the immediate cause of death is always the stop- 
page of the functions of one of three organs ; the cerebro- 
spinal nervous centre, the lungs, or the heart. Thus, a man 
may be instantly killed by such an injury to a part of the 
brain which is called the medulla oblongata {see 332), as 
may be produced by hanging, or breaking the neck. 

Or death may be the immediate result of suffocation by 
strangulation, smothering, or drowning; or, in other words, 
of stoppage of the respiratory functions. 

Or, finally, death ensues at once when the heart ceases 
to propel blood. These three organs — the brain, the lungs, 
and the heart — have been fancifully termed the tripod of 
life. 

In ultimate analysis, however, life has but two legs to 
stand upon, the lungs and the heart, for death through the 
brain is always the effect of the secondary action of the 
injury to that organ upon the lungs or the heart. The 
functions of the brain cease, when either respiration or 
circulation is at an end. But if circulation and respiration 
are kept up artificially, the brain may be removed without 
causing death. On the other hand, if the blood be not 
aerated, its circulation by the heart cannot preserve life ; 
and, if the circulation be at an end, mere aeration of the 
blood in the lungs is equally ineffectual for the prevention 
of death, 

35. Dissolution of the Body.— With the cessation of life, 
the every-day forces of the inorganic world no longer remain 
the servants of the bodily frame, as they were during life, 
but become its masters. Oxygen, the sweeper of the living 
organism, becomes the lord of the dead body. Atom by 
atom, the complex molecules of the tissues are taken to 
pieces and reduced to simpler and more oxidized sub- 
stances, until the soft parts are dissipated chiefly in the 



LIFE AND DEATH. 

form oi carbonic arid, ammonia, water, and soluble salts. 

and the bones and teeth alone remain. But not even tfa 
dense and earthy structures are competent to offer a per- 
manent resistance to water and air. Sooner or later the 
animal basis which holds together the earthy salts decom- 
ses and dissolves — the solid structures become friable, 
and break down into powder. Finally, they dissolve and 
are diffused among the waters of the surface ot the globe, 
just as the gaseous products oi decomposition are die 
pated through its atmosphere. 

It is impossible to follow, with any degree of certainty, 
wanderings more varied and more extensive than those 
imagined by the ancient sages who held the doctrine ^i 
transmigration; but the chances are that, sooner or later, 

e, if not all, oi the scattered atoms will be gathered 
into new forms oi life. 

The sun's rays, acting through the vegetable world, 
build up some of the wandering molecules of carbonic arid, 
o{ water, of ammonia, and of salts, into the fabric of plants. 
The plants are devoured by animals, animals devour one 
another, man devours both plants and other animals; and 
hence it is very possible that atoms which once formed an 
integral part oi the busy brain of Julius QsBSar may now 
enter into the composition of Qsosar the negro in Alabama, 
and of Osesar the house-dog in an English homestead. 

And thus there is sober truth in the words which 
Shakespeare puts into the mouth of Ejamlet: 

Imperial Caesar, dead an! by, 

■ 
Oh that that earth, which kept the world in ..••■ 
ShouJd patch a wall. winter's flaw ! ■ 



34 ELEMENTARY PHYSIOLOGY. 

CHAPTER II. 

THE VASCULAR SYSTEM AND THE CIRCULATION. 

Section I. — The Vascular System. 

36. Capillary Vessels.— Almost all parts of the body are 
vascular ; that is to say, they are traversed by minute arid 
, very close-set canals, which open into one another so as to 
constitute a small-meshed net-work, and confer upon these 
parts a spongy texture. The canals, or rather tubes, are 
provided with distinct but very delicate walls, composed 
of a structureless membrane (Fig. 5, #), in which at inter- 
vals small oval bodies (Fig. 5, #), termed nuclei (see 340), 
are embedded. 

These tubes are the capillaries. They vary in diameter 
from ^oVo th to j^Vo^ 1 of an inch ; they are sometimes dis- 
posed in loops, sometimes in long, sometimes in wide, 
sometimes in narrow meshes ; and the diameters of these 
meshes, or, in other words, the interspaces between the 
capillaries are sometimes hardly wider than the diameter of 
a capillary, sometimes many times as wide (see Figs. 19, 
25, 26, 40, 41, 46). These interspaces are occupied by the 
substance of the tissue which the capillaries permeate (Fig. 
5, c), so that the ultimate anatomical components of every 
part of the body are, strictly speaking, outside the vessels, 
or extra-vascular. 

But there are certain parts which, in another and broader 
sense, are also said to be extra-vascular or nonvascular. 
These are the epidermis and epithelium, the nails and hairs, 
the substance of the teeth, and the cartilages ; which may 
and do attain a very considerable thickness or length, and 
yet contain no vessels. However, as we have seen that all 
the tissues are really extra-vascular, these differ only in de- 
gree from the rest. The circumstance that all the tissues 



THE VASCULAR SYSTEM. 



35 



are outside the vessels by no means interferes with their 
being- bathed by the fluid which is inside the vessels. In 
fact, the walls of the capillaries are so exceedingly thin 






-/ 



^ d 
-c 




Fig. 



Pig. 6. 



Fiu 5l — Diagrammatic representation of a capillary soon from above and in section: 
a. the wall of to i capillary with &, the nuclei ; <• nuclei belonging to the connective tis- 
sue in which th • c ipillary is suppose 1 to be lying; >'. the canal of the capillary. 

FL r . *>. — Diagrammatic representation of the structure of o small artery : c epithe- 
lium : b. the so-calle I basement membrane : c the circular non-striated muscular fibres, 
■ At of fibrous tissue with nuclei/'. 

that their fluid contents readily exude through the delicate 
membrane of which they are composed, and irrigate the 
tissues in which they lie, 

37. The Smaller Arteries and Veins. — Of the capillary 
lubes thus described, one kind contains, during life, the 
re 1 fluid, blood, while the others are filled with a pale, 
watery, or milky fluid, termed lymph, or chyle. The capil- 
laries, whirh contain blood, are continued on different sides 
into somewbal larger tubes, with thicker walls, which are 
the smallest arteries and veins. 

The mere faci thai the walls of these vessels are thicker 
than those of the capillaries constitutes an important differ- 
ence between the capillaries and the small arteries and 



36 ELEMENTARY PHYSIOLOGY. 

veins ; for the walls of the latter are thus rendered far 
less permeable to fluids, and that thorough irrigation of 
the tissues, which is effected by the capillaries, cannot be 
performed by them. 

The most important difference between these vessels 
and the capillaries, however, lies in the circumstance that 
their walls are not only thicker, but also more complex, 
being composed of several coats, one, at least, of which is 
muscular. The number, arrangement, and even nature of 
these coats differ according to the size of the vessels, and 
are not the same in the veins as in the arteries, though the 
smallest veins and arteries tend to resemble each other. 

38. Structure of the Arteries. — If we take one of the 
smallest arteries, we find, first, a very delicate lining of 
cells constituting a sort of epithelium (Fig. 6, a). Outside 
this (separated from it by a structureless membrane, Fig. 
6, b) comes the muscular coat of the kind called plain or 
non-striated muscle {see 355), made up of flattened, spin- 
dle-shape bands or fibres, which are wrapped round the 
vessel (Fig. 6, c). 

Outside the muscular coat is a sheath of fibrous or con- 
nective tissue (Fig. 6,/*). 

In the smallest arteries there is but a single layer of 
these muscular fibres, encircling the vessel like a series of 
rings ; but, in the larger arteries, there are several layers 
of circular muscular fibres, variously bound together with 
fibrous and elastic tissue, though, as the vessels get larger, 
the quantity of muscular tissue in them gets relatively less. 

39. Contractility of the Vascular Fibres. — Now, these 
plain muscular fibres possess that same power of contrac- 
tion, or shortening in the long, and broadening in the 
narrow, directions which, as was stated in the preceding 
chapter, is the special property of muscular tissue. And, 
when they exercise this power, they, of course, narrow the 
calibre of the vessel, just as squeezing it in any other way 
would do ; and this contraction may go so far as, in some 



THE VASCULAR SYSTEM. 37 

cases, to reduce the cavity of the vessel almost to nothing, 
and to render it practically impervious. 

40. Circulating Vessels controlled by Nerves. — The state 
of contraction of these muscles of the small arteries and 
veins is regulated, like that of other muscles, by their 
nerves; or, in other words, the nerves supplied to the 

—els determine whether the passage through these tubes 
should be wide and free, or narrow and obstructed. Thus, 
while the small arteries and veins lose the function, which 
the capillaries possess, oi directly irrigating the tissues by 
transudation, they gain that of regulating the supply of 
fluid to the irrigators, or capillaries themselves. The eon- 
traction, or dilatation, of the arteries which supply a set 
of capillaries, comes to the same result as lowering or rais- 
ing the sluice-gates of a svstem of irrigation-canals. 

41. Differences between Arteries and Veins. — The small- 
er arteries and veins severally unite into, or are branches 
of, larger arterial or venous trunks, which again spring 
fmm or unite into still larger ones, and these, at length, 
communicate by a few principal arterial and venous trunks 
with the heart. 

The smallest arteries and veins, as we have seen, are 
similar in structure, but the larger arteries and veins differ 
widely ; for the larger arteries have walls so thick and 
Stout that they do not sink together when empty; and 
this thickness and stoutness arises from the circumstance 
that not only is the muscular coat very thick, but that, in 
addition, and more especially, several layers of a highly- 
elastic, s _. fibrous Bubstance become mixed up with 
the muscular layers. Thus, when a large artery is pulled 
out and ht go, it stretches and returns to its primitive 
dimensions, almost like a piece of India-rubber. 

The larger veins, on the other hand, contain but little 

of either elastic or muscular tissue. Hence, their walls are 

thin, and they collapse wln-n empty . 

This is one great difference between the larger arteries 



38 ELEMENTARY PHYSIOLOGY. 

and the veins ; the other is the presence of what are termed 
valves in a great many of the veins, especially in those 
which lie in muscular parts of the body. They are absent 
in the largest trunks, and in the smallest branches, and in 
all the divisions of the portal, pulmonary, and cerebral 
veins. 

42. Action of the Valves of the Veins. — These valves 
are pouch-like folds of the inner wall of the vein. The 
bottom of the pouch is turned towards those capillaries 
from which the vein springs. The free edge of the pouch 
is directed the other way, or towards the heart. The action 
of these pouches is to impede the passage of any fluid from 
the heart towards the capillaries, while they do not inter- 
fere with fluid passing in the opposite direction (Fig. 7). 
The working of some of these valves may be very easily 
demonstrated in the living body. When the arm is bared, 
blue veins may be seen running from the hand, under the 
skin, to the upper arm. The diameter of these veins is 
pretty even, and diminishes regularly towards the hand, so 
long as the current of the blood, which is running in them, 
from the hand to the upper arm, is uninterrupted. 



H 



Fig. 7. 
Diagrammatic Sections op Veins with Valves. 

In the upper, the blood is supposed to be flowing 1 in the direction of the arrow, 
toward the heart ; in the lower, the reverse way. C, capillary side ; II, heart side. 

But, if a finger be pressed upon the upper part of one 
of these veins, and then passed downwards along it, so as 
to drive the blood which it contains backwards, sundry 
swellings, like little knots, will suddenly make their ap- 



THE VASCULAR SYSTEM 39 

pea ranee at several points in the length of the vein, where 
nothing of the kind was visible before. These swellings 
are simply dilatations of tin 4 wall of the vein, caused by 
the pressure o£ the blood on that Avail, above a valve 
which opposes its backward progress. The moment the 
backward impulse ceases, the blood flows on again; the 
valve, swinging back towards the wall of the vein, affords 
no obstaele to its progress, and the distention caused by 
its pressure disappears (Fig. 7). 

The only arteries which possess valves are the primary 
trunks — the aorta and pulmonary artery — which spring 
from the heart, and they will be best considered with the 
latter organ. 

43. The Lymphatics. — Besides the capillary net-work 
and the trunks connected with it, which constitute the 
blood-vascular system, all parts of the body which possess 
blood-capillaries — except the, brain and spinal cord, the 
eyeball, the gristles, tendons, and perhaps the bones ' — 
also contain another set of what are termed lymphatic 
capillaries, mixed up with those of the blood-vascular sys- 
tem, but not directly communicating with them, and, in 
addition, differing from the blood-capillaries in being con- 
nected with larger vessels of only one kind. That is to 
Bay, they open only into trunks which carry fluid away 
from them, there being no large vessels which bring any 
thing to them. 

These trunks further resemble the small veins in being 
abundantly provided with valves, which freely allow of the 
passage of liquid from the Lymphatic capillaries, but ob- 
struct the flow of any thing the other way. But the lym- 
phatic trunks differ from the veins, in that they do not 
rapidly unite into larger and larger trunks, which presenl 
a continually increasing calibre, and allow of a flow with- 
out interruption to the heart. 

ible that these exception are apparent rattier than real, bat the question 
rily decided. 



40 



ELEMENTARY PHYSIOLOGY. 



On the contrary, remaining nearly of the same size, 
they, at intervals, enter and ramify in rounded bodies 
called lymphatic glands ', whence new lymphatic trunks 
arise (Fig. 8), In these glands the lymphatic capillaries 
and passages are closely interlaced with blood-capillaries. 




Fig. 8. 

The Lymphatics of the Feont of the Right Arm. 

g Lymphatic glands, or ganglia, as they are sometimes called. These ganglia are 
not to be confounded with nervous ganglia. 



Sooner or later, however, the great majority of the 
smaller lymphatic trunks pour their contents into a tube, 
which is about as large as a crow-quill, lies in front of the 
backbone, and is called the thoracic duct This opens at 
the root of the neck into the conjoined trunks of the great 
veins which bring back the blood from the left side of the 
head and the left arm (Fig. 9). The remaining lymphatics 



THE VASCULAR SYSTEM. 



41 



are connected by a common canal with the corresponding 

vein on the right side. 

Where the principal trunks of the lymphatic system 
open into the veins, valves are placed, which allow T of the 




Fig. 9. 
Tiif. THOB \< I- Dr< t 

The Thoracic Dad occupies the middle of the figure. It Hea upon the spinal eol« 
umn. at the sid.-> of which ire seen portiona of the hi.- i I >. 

'i. the receptacle of the chyle : 2>. the trunk of the thoracic duet, opening at e Into 

of the left iugular | r | and Bubelaylan {g) reins aa they unite Into the left 

Innominate win. which baa been cut acroat to -how the thoracic duct running behind 

it: <i, lymphatic riande placed In the lumbar reglona; //. the luperior vena cava formed 

by the junction of the right and left Innominate 



42 ELEMENTARY PHYSIOLOGY. 

passage of fluid only from the lymphatic to the vein. Thus 
the lymphatic vessels are, as it were, a part of the venous 
system, though, by reason of these valves, the fluid which 
is contained in the veins cannot get into the lymphatics. 
On the other hand, every facility is afforded for the pas- 
sage into the veins of the fluid contained in the lymphatics. 
Indeed, in consequence of the numerous valves in the lym- 
phatics, every pressure on and contraction of their walls, 
not being able to send the fluid backward, must drive it 
more or less forward towards the veins. 

44. The Lacteals. — The lower part of the thoracic duct 
is dilated, and is termed the receptacle, or cistern, of the 
chyle (a, Fig. 9). In fact, it receives the lymphatics of the 
intestines, which, though they differ in no essential respect 
from other lymphatics, are called lacteals, because, after a 
meal containing much fatty matter, they are filled with a 
milky fluid, which is termed the chyle. The lacteals, or 
lymphatics of the small intestine, not only form net-works 
in its walls, but send blind prolongations into the little 
velvety processes termed villi, with which the mucous 
membrane of that intestine is beset {see 189). The trunks 
which open into the net-work lie in the mesentery (or mem- 
brane which suspends the small intestine to the back wall 
of the abdomen), and the glands through which these trunks * 
lead are hence termed the mesenteric glands. 

Section II. — Connections and Structure of the Heart. 

45. The Heart and the Great Vessels. — It will now be 
desirable to take a general view of the arrangement of all 
these different vessels, and of their relations to the great 
central organ of the vascular system — the heart (Fig. 10). 

All the veins of every part of the body, except the 
lungs, the heart itself, and certain viscera of the abdomen, 
join together into larger veins, which, sooner or later, open 
into one of two great trunks (Fig. 10, ~V.CS., V.C.I.), 
termed the superior and the inferior vena cava, which 



CONNECTION AND STRUCTURE OF THE HEART 

debouch into tlie upper, or broad end of the right half of 
the heart. 




DIA-VRa* r, T T7TT. TTf.aP.T an?' FHU, WTTn T: 

VIEWED FE"M BEHIND. M THAT THE OBSERVES CORSE- 

VOSTM WITH THE L B THE HeaBT IN THE PlICTiW 

left auricle : Z. PI left ventricle : J"., aorta : A >. arteries to the upper part of 
the body : A 2 . arteries to the lower part I , hepatic artery, which 

pftes the Hver wtth part of it* \>V > • I *. 

Teins of the lower par: 7, in- 

ferior vena cava ; irht auricle : Fi. I", rUrbt Tent: 

pulmonary arterr : Lg^ hi: _ r„ lacteal* 

phat • borackr duct : Al~ alimentary cana. . arrows indicate 

the course of the blood lymph, ami chyle. The vessels which contain arterial blood 
nave dark coowura. while tome which carry veooua blood hare light contours. 



44 ELEMENTARY PHYSIOLOGY. 

All the arteries of every part of the body, except the 
lungs, are more or less remote branches of one great trunk 
— the aorta (Fig, 10, Ao*\ which springs from the lower 
division of the left half of the heart. 

The arteries of the lungs are branches of a great trunk 
(Fig. 10, P. A.), springing from the lower division of the 
right side of the heart. The veins of the lungs, on the con- 
trary, open by four trunks into the upper part of the left 
side of the heart (Fig. 10, _P. V.). 

Thus the venous trunks open into the upper division of 
each half of the heart ; those of the body in general into 
that of the right half; those of the lungs into that of the 
left half; while the arterial trunks spring from the lower 
moieties of each half of the heart, that for the body in 
general from the left side, and that for the lungs from the 
right side. 

Hence it follows that the great artery of the body, and 
the great veins of the body, are connected with opposite 
sides of the heart ; and the great artery of the lungs, and 
the great veins of the lungs also, with opposite sides of 
that organ. On the other hand, the veins of the body 
open into the same side of the heart as the artery of the 
lungs, and the veins of the lungs open into the same side 
of the heart as the artery of the body. 

46. Coronary Arteries and Vein. — The arteries which 
open into the capillaries of the substance of the heart are 
called coronary arteries, and arise, like the other arteries, 
from the aorta, but quite close to its origin, just beyond 
the semilunar valves. But the coronary vein, which is 
formed by the union of the small veins which arise from 
the capillaries of the heart, does not open into either of 
the vense cavae, but pours the blood which it contains di- 
rectly into the division of the heart into which these cavoe 
open ; that is to say, into the right upper division (Fig. 
17, b). 

47. Hepatic Vessels. — The abdominal viscera referred to 



CONNECTIONS AND STRUCTURE OF THE HEART. 45 

above, the veins of which do not take the usual course, are 
the stomach, the intestines, the spleen, and the pancreas. 
These veins all combine into a single trunk, which is termed 
the vena porta (Fig, 10, I ./*.), but this trunk does not 
open into the vena cava inferior. On the contrary, having 
reached the liver, it enters the substance of that organ, and 
breaks up into an immense multitude of capillaries, which 
ramify through the liver, and become connected with those 
into which the artery of the liver, called the Jiepatic artery 
(Fig. 10, H.A.), branches. From this common capillary 
mesh-work veins arise, and unite, at length, into a single 
trunk, the Aq cUic V( in (Fig. 10, If. K), which emerges from 
the liver, and opens into the inferior vena cava. The por- 
tal vein is the only great vein in the body which branches 
(nit and becomes continuous with the capillaries of an op 
gan, like an a it cry. 

48. The Heart— The heart (Figs. 11 and 13), to which 
all the vessels in the body have now been directly or in- 
directly traced, is an organ, the size of which is usually 
roughly estimated as equal to that of the closed fist of the 
person to whom it belongs, and which has a broad end 
turned upwards and backwards, and rather to the right side, 
called its base : and a pointed end, which is called its 
"/"./'. turned downwards and forwards, and to the left side, 

els to lie opposite the interval between the fifth and 
sixth ribs. 

It is lodged between the lungs, nearer the front than 
the buck wall of the chest, and is inclosed in a sort of 
double bag — the pericardium (Fig. 12, ;>.). One-half of 
the double bag is closely adherent to the heart itself, form- 
ing a thin coat up-.n its outer surface. At the base of the 

heart, this half of the bag passes on to the greal vessels 
which spring from, or open into, thai organ; and becomes 

Continuous with the other half, whieh looselv envelops the 

hearl and the adherent half of the ban-. Between the two 
layers of the pericardium, consequently, there is a com- 



46 



ELEMENTARY PHYSIOLOGY. 



pletely-closed, narrow cavity, lined by an epithelium, and 
secreting into its interior a small quantity of clear fluid. 1 

Tr 




Fig. 11. 

Heart of Sheep, as seen after Kemoval from the Body, lying upon the Two 
Lungs. The Pericardium has been cut away, but no other Dissection made. 

JR. A., auricular appendage of right auricle: L.A., auricular appendage of left au- 
ricle; E. V., right ventricle ; L.V., left ventricle; S. Y.C., superior vena cava; I.V.C.. 
inferior vena cava ; P.A., pulmonary artery ; Ao., aorta ; A'o\ innominate branch from 
aorta dividing into subclavian and carotid arteries; X., lung; 7>., trachea. 1. Solid 
cord often present, the remnant of a once open communication between the pulmonary 
artery and aorta. 2. Masses of fat at the bases of the ventricle hiding from view the 
greater part of the auricles. 3. Line of fat marking the division between the two ven- 
tricles. 4. Mass of fat covering end of trachea. 

1 This fluid, like that contained in the peritoneum, pleura, and other shut sacs of 
a similar character to the pericardium, is sometimes called serum; whence the mem- 
branes forming the walls of these sacs are frequently termed serous membranes. 



CONNECTIONS AND STRUCTURE OF THE HEART. 4 7 

The outer layer of the pericardium is firmly connected be- 
low with the upper surface oi" the diaphragm. 

Bui the heart cannot be said to depend altogether upon 
tin 4 diaphragm for support, inasmuch as the great vessels 



-, f*\ 




Fhs. 12. 

TkAXB - HOH OF tiii: <"hf>t. with tiik Heart and Luifefl r.v Place, 

i A littk- diagrammatic.) 

D. V the backbone; .(".. .(" . aorta, the top of its arrh 

_ ■ .. Buperior vena cava: /'.A. pulmonary artery, di- 

lumr: L.P.. I!. P.. left and right pulmonary veins; Br., 

lii: R.L.. L.L.. right an<l left lurnr- : (£, the gullet <»r oesophagus; p., outer bag 

riearahmi : y><- the two layers of pleura ; >'.. asygOB veto. 



which is<ue tV >m or enter it — and for the most part pass 
upwards from its base — help to suspend and keep it in place. 
49. The Auricles and Ventricles. — Thus the heart is 
Tt-d, outside, by one layer of the pericardium, Inside, 
it contains two great cavities or "divisions," as they have 
:i termed above, completely separated by a fixed par- 
tition which extends from the base to the apex of the heart ; 
and, [uently, having no direct communication with 

one another. Each of these two great cavities is further 
subdivided, not longitudinally hut transversa ly, by a mov- 
able partition. The cavity above the transverse partition, 
on cadi Bide, is called the auricli : the cavity below, the 
ventricli — right or left as the case may be. 



48 



ELEMENTARY PHYSIOLOGY. 



Each of the four cavities has the same capacity, and is 
capable of containing from four to six cubic inches of water. 
The walls of the auricles are much thinner than those of 
the ventricles. The wall of the left ventricle is much 



r.j.v: c T c 




Fig. 13. 
The Heart, Great Vessels, and Lungs. (Front View.) 

R, V., right ventricle; L.V., left ventricle; R.A., right auricle; L.A., left auricle; 
Ao., aorta; P.A., pulmonary artery ; P. F., pulmonary veins ; R.L., right lung: Z.Z., 
left lung ; V.S.. vena cava superior ; 8. <?., subclavian vessels ; C, carotids ; R.J. V., and 
L.J. V., right and left jugular veins; F./., vena cava inferior; T 7 ., trachea; £., bronchi. 
All the great vessels but those of the lungs are cut. 

thicker than that of the right ventricle ; but no such dif- 
ference is perceptible between the two auricles (Figs. 14 
and 15, 1 and 3). 

50. Their Unequal Work. — In fact, as we shall see, the 
ventricles have more work to do than the auricles, and the 
left ventricle more to do than the right. Hence the ven- 
tricles have more muscular substance than the auricles, and 
the left ventricle than the right ; and it is this excess of 
muscular substance which gives rise to the excess of thick- 
ness observed in the left ventricle. 

51. Muscular Fibres and Fibrous Rings. — The muscular 
fibres of the heart are not smooth, nucleated bands, like 



CONNECTIONS AND STRUCTURE OF THE HEART. 49 

those of the vessels, but are bundles of* transversely- striped 
fibres, and resemble those of the chief muscles of the body, 
except that they have no sheath, or sarcolemma, such as 

we shall find to exist in the latter. " 



S.V.C 




Fi». 14. 

Right Side <>f tut. Heart or \ Snr.r.T\ 

R.A.. cavity of rijrht auricle : 8. V.i '■• superior vena cava ; /. ]'.('. inferior vena cava 
(a style hai 1 through each of these); </. a styk passed from the auricle to 

the ventricle through the auriculo-ventricular orifice; i>, a style passed into the coro- 
nary v. -in. /.'. V.. cavity of right ventricle: t.r.. t.r.. n\o flaps oi the tricuspid valve; 
the third is dknlj seen Dehind thein. the style a passing betareen the three. Between 
d attached to them by chorda tendiiu p, is Been a papillary muscle, 
j>j>.. cut away from it- attachment to thai portion of the wall of the ventricle which has 
the ventricle terminates somewhat Bke a funnel In the pulmo- 
nary artery. I'. A. One of tip pockets oi the semilunar valve, *.«.. is seen In Itsen- 
r. another partially. I. The wall of the ventricle cut across 2. The position of the 
■nrieuJo- ventricular ring ;'.. The wall of the auricle. 4. Masses of nil lodged between 
the auricle arid pulmonary artery. 



Almost the whole m«'i>s of the heart is made np nf these 
muscular fibre-, which have a very remarkable and complex 
4 



50 ELEMENTARY PHYSIOLOGY. 

arrangement. There is, however, an internal membranous 
and epithelial lining, called the endocardium / and, at the 
junction between the auricles and ventricles, the apertures 
of communication between their cavities, called the au- 
riculo-ventricular apertures, are strengthened by fibrous 
rings. To these rings the movable partitions, or valves, 
between the auricles and ventricles, the arrangement of 
which must next be considered, are attached. 

52. Valves of the Heart ; their Structure and Action. — 
There are three of these partitions attached to the circum- 
ference of the right auriculo-ventricular aperture, and two 
to that of the left (Figs. 14, 15, 16, 17, t v 9 m v). Each is 
a broad> thin, but very tough and strong triangular fold of 
the endocardium, attached by its base, which joins on to 
its fellow, to the auriculo - ventricular fibrous ring ; and 
hanging with its point downwards into the ventricular cav- 
ity. On the right side there are, therefore, three of these 
broad, pointed membranes, whence the whole apparatus is 
called the tricuspid valve. On the left side there are but 
two, which, when detached from all their connections but 
the auriculo-ventricular ring, look something like a bishop's 
mitre, and hence bear the name of the mitral valve. 

The edges and apices of the valves are not completely 
free and loose. On the contrary, a number of fine but 
strong tendinous cords, called chorda? tendinece, connect 
them with some column-like elevations of the fleshy sub- 
stance of the walls of the ventricle, which are termed 
papillary muscles (Figs. 14 and 15, pp) ; similar column- 
like elevations of the walls of the ventricles, but, having 
no chordm tendinece attached to them, are called columnar 
carneoe. 

It follows, from this arrangement, that the valves op- 
pose no obstacle to the passage of fluid from the auricles 
to the ventricles ; but, if any should be forced the other 
way, it will at once get between the valve and the wall 
of the heart, and drive the valve backwards and upwards. 



CONNECTIONS AND STRUCTURE OF THE HEART. 5] 

Partly because they a on meet in the middle and oppose 
one another's action, and partly because the c/ior 

bold their edges and prevent th back 

too far, the valves, thus I ► the for- 

mation of a complete t: partition between the 




■ 



Left mpe of ttte 1 1 

P. . pohnounr >'.vn by 

••in which, though it hfl 
with thus laying i 

I 
: /'/'. ptpfDaiy mi the rentrlcfte 

isaed from 
/' A . [.Tilrnonar 

: :iuri<ul<»-v»ritri< 
auricular wall cut .up >-- J . MUms of fkt around baa .«/« FL r . 1 



52 



ELEMENTAKY PHYSIOLOGY. 



ventricle and the auricle, through which no fluid can pass. 
Where the aorta opens into the left ventricle, and where 
the pulmonary artery opens into the right ventricle, another 
valvular apparatus is placed, consisting, in each case, of 
three pouch-like valves, called the semilunar valves (Fig\ 
14, s.v.; Figs, 16 and 17, Ao.P.A.), which are similar to those 



AO 



7?A 




LAV 



Fig. 1G. 

View of the Oeifices of the Heaet feom below, the whole of the Ventri- 
cles HAVING BEEN CUT AWAY. 

JR.A. V., right auriculo- ventricular orifice, surrounded by the three flaps t.v. 1, t.v. 2, 
t.v. 3. of the tricuspid valve : these are stretched by weights attached to the c/wrdce 
tenclinece. L.A. F., left auriculo-ventricular orifice, surrounded in the same way by 
the two flaps, m/c. 1, m.v. 2, of mitral valve; P. A., the orifice of pulmonary artery, 
the semilunar valves having 1 met and closed together ; Ao., the orifice of the aorta. 
with its semilunar valves. The shaded portion, leading from R.A. V. to P. A., repre- 
sents the funnel seen in Fig. 14. 

of the veins. But, as they are placed on the same level and 
meet in the middle line, they completely stop the passage 
when any fluid is forced along the artery towards the heart. 
On the other hand, these valves flap back, and allow any 
fluid to pass from the heart into the artery, with the utmost 
readiness. 



CONNECTIONS AND STRUCTURE OF THE HEART. 



53 



The action of the anrienlo-ventricnlar valves may be 
demonstrated with great ease od a sheep's heart, in which 
the aorta and pulmonary artery have been tied and the 
greater part of the auricles cut away, by pouring water 
into the ventricles through the auriculo-ventricular aper- 
ture. The tricuspid and mitral valves then usually become 
dosed by the upward pressure of the water which gets be- 
hind them. Or, if the ventricles be nearly filled, the valves 
may be made to come together at once by gently squeezing 
the ventricles. In like manner, if the base of the aorta, or 
pulmonary artery, be cut out of the heart, so as not to in- 



FA 




ZAY 



Fm. it. 

The Oftmcn of the Heart BRH from ABOVE, the kUBlOUBB and GSEAT Vr- 

raaora i 01 away. 

it- semilunar valves ; An., aorta, da /*..!. P., richt 

naricul" . with the three flaps i/' - . 1. •_'. 8) <>t* tricuspid valve. I. A. r.. 

left aur, Mith m >. l and i. flaps of mitral valve : &, Btyle passed 

nary v. -in. On the left part of I. A. r. the section of the anricle la carried 

- : hence the toothed appearance <lu«- t<> the portion! 

in n-li'-: 



jure the semilunar valves, water poured into the upper 
ends of the vessel will cause its valves to close tightly, 

and allow nothing to flow out after the first moment. 



54 ELEMENTARY PHYSIOLOGY. 

Thus the arrangement of the auriculo-ventricular valves 
is such, that any fluid contained in the chambers of the 
heart can be made to pass through the auriculo-ventricular 
apertures in only one direction : that is to say, from the 
auricles to the ventricles. On the other hand, the arrange- 
ment of the semilunar valves is such that the fluid con- 
tents of the ventricles pass easily into the aorta and pul- 
monary artery, while none can be made to travel the other 
way from the arterial trunks to the ventricles. 

53. Rhythm of its Movement— Systole and Diastole. 
— Like all other muscular tissues, the substance of the heart 
is contractile; but, unlike most muscles, the heart con- 
tains within itself a something which causes its different 
parts to contract in a definite succession and at regular in- 
tervals. 

If the heart of a living animal be removed from the 
body, it will go on pulsating for a longer or shorter time, 
much as it did while in the body. And careful attention 
to these pulsations will show that they consist of: 1. A 
simultaneous contraction of the walls of both auricles ; 2. 
Immediately following this, a simultaneous contraction of 
the walls of both ventricles ; 3. Then comes a pause, or 
state of rest ; after which the auricles and ventricles con- 
tract again in the same order as before, and their contrac- 
tions are followed by the same pause as before. 

If the auricular contraction be represented by A v , the 
ventricle by V w , and the pauses by — , the series of actions 
will be as follows: A~ V~ — ; A" V~ — ; AV^ — ; etc. 
Thus, the contraction of the heart is rhythmical, two short 
contractions of its upper and lower halves respectively be- 
ing followed by a pause of the whole, which occupies about 
as much time as the two contractions. 

The state of contraction of the ventricle or auricle is 
called its systole ; the state of relaxation, during which it 
undergoes dilatation, its diastole. 



WORKING OF THE HEART AND VESSELS. 55 

Section III. — Working of the Heart and Vessels. 

54. Working of the Heart. — Having now acquired a 
notion of the arrangement of the different pipes and reser- 
voirs of the circulatory system, of the position of the valves, 
and of the rhythmical contractions of the heart, it will be 
easy to comprehend what must happen if, when the whole 
apparatus is full of blood, the first step in the pulsation of 
the heart occurs and the auricles contract. 

By this action each auricle tends to squeeze the fluid 
which it contains out of itself in two directions — the one 
towards the great veins, the other towards the ventricles ; 
and the direction which the blood, as a whole, will take, 
will depend upon the relative resistance offered to it in 
these two directions. Towards the great veins it is re- 
sisted by the mass of the blood contained in the veins. 
Towards the ventricles, on the contrary, there is no resist- 
ance worth mentioning, inasmuch as the valves are open, 
the walls of the ventricles, in their uncontracted state, are 
flaccid and easily distended, and the entire pressure of the 
arterial blood is taken off by the semilunar valves, which 
a!<' necessarily closed. 

Therefore, when the auricles contract, only a very little 
of the fluid which they contain will flow back into the veins, 
and the great proportion will pass into and distend the 
ventricles. As the ventricles fill and begin to resist fur- 
ther distention, the blood, getting behind the auriculo-ven- 
tricular valves, will push them towards one another, and 
almost -hut them. The auricles now cease to contract, a nd 
immediately thai their walls relax, fresh blood flows from 

the great veins and slowly distends them again. 

But, the moment the auricular systole is over, the ven- 
tricular systole begins. The walls of each ventricle con- 
trad vigorously, and the first effect of that contraction is 
to shut the auriculo-ventricular valves completely and to 
stop all egress towards the auricle. The pressure upon the 



56 ELEMENTARY PHYSIOLOGY. 

valves becomes very considerable, and they might even be 
driven upwards, if it were not for the chordm tendinece 
which hold down their edges. 

As the contraction continues and the capacities of the 
ventricles become diminished, the points of the wall of the 
heart to which the chordm tendinece are attached approach 
the edges of the valves ; and thus there is a tendency to 
allow of a slackening of these cords, wmich, if it really took 
place, might permit the edges of the valves to flap back and 
so destroy their utility. This tendency, however, is coun- 
teracted by the chordm tendinece being connected, not 
directly to the walls of the heart, but to those muscular 
pillars, the papillary muscles, which stand out from its sub- 
stance. These muscular pillars shorten at the same time 
as the substance of the heart contracts ; and thus, just so 
far as the contraction of the walls of the ventricles brings 
the papillary muscles nearer the valves, do they, by their 
own contraction, pull the chordae tendinem as tight as 
before. 

By the means which have now been described, the fluid 
in the ventricle is debarred from passing back into the au- 
ricle ; the whole force of the contraction of the ventricular 
walls is therefore expended in overcoming the resistance 
presented by the semilunar valves. This resistance has 
several sources, being the result, partly, of the weight of 
the vertical column of blood which the valves support ; 
partly, of the reaction of the distended elastic walls of the 
great arteries, and partly, of the friction and inertia of the 
blood contained in the vessels. 

It now becomes obvious why the ventricles have so 
much more to do than the auricles, and why valves are 
needed between the auricles and ventricles, while none are 
wanted between the auricles and the veins. 

All that the auricles have to do is to fill the ventricles, 
which offer no active resistance to that process. Hence 
the thinness of the walls of the auricles, and hence the 



WORKING OF THE HEART AND VESSELS. 5^ 

needlessness of any auriculo-venous valve, the resistance 
on the side of the ventricle being so insignificant that it 
gives way, at once, before the pressure of the blood in the 
veins. 

On the other hand, the ventricles have to overcome a 
_ a resistance in order to force fluid into elastic tubes 
which are already full ; and, if then 1 were no auriculo-ven- 
tricular valves, the fluid in the ventricles would meet with 
less obstacle in pushing its way backwards into the auricles 
and thence into the veins, than in separating 1 the semilunar 
valves. Hence the necessity, firstly, of the auriculoyen- 
tricular valves; and, secondly, of the thickness and strength 
of the walls oi the ventricles. And since the aorta, sys- 
temic arteries, capillaries, and veins, form a much larger 
•in of tubes, containing more fluid and offering more 
resistance than the pulmonary arteries, capillaries, and 
veins, it follows that the left ventricle needs a thicker 
muscular wall than the right. 

55. The Working of the Arteries. — Tims, at every Bys- 
of the auricles, the ventricles are filled and the auricles 
emptied, the latter being slowly refilled by the pressure of 
the fluid in the great veins, which is amply sufficient to 
overcome the passive resistance of the relaxed auricular 
walls. And, at every systole of the ventricles, the arterial 
systems of the body and lungs receive the contents of these 
and the nearly-emptied ventricles remain ready 
to he refilled by the auricles. 

We must cow consider what happens in the arteries. 

When the contents of the ventricles are suddenly forced 
into th«-'' tubes (which, it must he recollected, are already 
full), a shock IS given to the entire mass of fluid which 

they contain. Thi> shock i- propagated almost instanta- 
neously throughout the fluid, becoming fainter and fainter 
in proportion to the increase of th» mass of the blood in the 
capillaries, until it finally ceases to be discernible. 

If the vessels were tub rigid material, like gas- 



58 ELEMENTARY PHYSIOLOGY. 

pipes, the fluid which the arteries contain would be trans- 
ported forward as far as this impulse was competent to 
carry it, at the same instant as the shock, throughout their 
whole extent. And, as the arteries open into the capilla- 
ries, the capillaries into the veins, and these into the heart, 
a quantity of fluid exactly equal to that driven out of the 
ventricles would be returned to the auricles, almost at the 
same moment that the ventricles contract. 

However, the vessels are not rigid, but, on the contrary, 
very yielding tubes ; and the great arteries, as we have 
seen, have especially elastic walls. What happens, then, 
when the ventricular systole takes place, is: firstly, the 
production of the general slight and sudden shock already 
mentioned ; and, secondly, the dilatation of the great ar- 
teries by the pressure of the increased quantity of blood 
forced into them. 

But, when the systole is over, the force stored up in the 
dilated arterial walls, in the shape of elastic tension, comes 
into play and exerts a pressure on the fluid — the first effect 
of which is to shut the semilunar valves ; the second, to 
drive a certain quantity of the fluid from the larger arteries 
along* the smaller ones. These it dilates in the same fash- 
ion. The fluid at length passing into the capillaries, the 
ejection of a corresponding quantity of fluid from them into 
the veins, and finally from the veins into the heart, is the 
ultimate result of the ventricular systole. 

56, The Beat of the Heart. — Several of the practical 
results of the working of the heart and arteries just de- 
scribed now become intelligible. For example, between 
the fifth and sixth ribs, on the left side, a certain move- 
ment is perceptible by the finger and by the eye, which is 
known as the beating of the heart. It is the result of the 
striking of the apex of the heart against the pericardium, 
and, through it, on the inner wall of the chest, at this point, 
at the moment of the systole of the ventricles. When the 
systole occurs, in fact, two things happen : in the first place, 



WORKING OF THE HEART AND VESSELS. 59 

as a result of the manner in which the muscular fibres of 
the heart are disposed, its apex bends upwards sharply ; 

and, in the second place, its front face is thrown a little 
downwards and forwards, in consequence o( the st retelling 
and elongation oi the aorta by the blood which is thrown 
into it. The result o( one or other, or both of these actions 
combined, is the upward and forward blow (A the apex of 
the heart which we feel. 

57. The Sounds of the Heart. — Secondly, if the ear be 
applied over the heart, certain sounds are heard, which re- 
cur with great regularity, at intervals corresponding with 
those between every two beats. First comes a longish dull 

id; then a short sharp sound; then a pause; then the 
long, then the sharp sound, then another pause; and so on. 
There are many different opinions as to the eause of the 
first sound, and perhaps physiologists are not yet at the 
bottom of the matter; though the more probable view is, 
that part of it is a muscular sound caused by the contrac- 
tion of the muscular fibres of the ventricle, and part is due 
to the tension of the auriculo-ventricnlar valves ; but the 

- on 1 Bound is without doubt, caused by the sudden clos- 
ure of the semilunar valves when the ventricular systole 
ends. That such is the case has been proved experiment- 
ally, by hooking back the semilunar valves in a living ani- 
mal, when tin second sound ceases at once. 

58. The Pulse.— Thirdly, if the finger be placed upon 
an artery, sir h as that at the wrist, what is termed the 
jPttZft will be felt ; that is to say, tin* elastic artery dilates 

- ..'what, at regular intervals, which answer to the beat- 
ings of the heart The pulse which is fell by the finger, 
bow tea not correspond precisely with the beat of the 
heart, but tak<-< place a little after it, and the interval ifl 
longer the greater the distance of the artery from the hearth 
The beat of tin- artery on the inner side of the ankle, for 

mple, is a little later than the beat of the artery in the 
oh-. 



60 ELEMENTARY PHYSIOLOGY. 

The reason of this is that the sense of touch by finger 
is only delicate enough to distinguish the dilatation of the 
artery by the wave of blood, which is driven along it by 
the elastic reaction of the aorta, and is not competent to 
perceive the first shock caused by the systole. But, if, in- 
stead of the fingers, sufficiently delicate levers were made 
to rest upon any two arteries, it would be found that the 
pulse really begins at the same time in both, the shock of 
the systole making itself felt all over the vascular system 
at once ; and that it is only the actual dilatation of the ar- 
terial walls, which, traveling in the form of a wave from 
the larger to the smaller arteries, takes longer to reach and 
distend the more distant branch. 

59. Jetting of Blood from Cut Arteries. — Fourthly, when 
an artery is cut, the outflow of the fluid which it contains 
is increased by jerks, the intervals of which correspond with 
the intervals of the beats of the heart. The cause of this 
is plainly the same as that of the pulse ; the force which 
would be employed in distending the walls of the artery, 
were the latter entire, is spent in jerking the fluid out when 
the artery is cut. 

60. Why the Capillaries are pulseless. — Fifthly, under 
ordinary circumstances, the pulse is no longer to be de- 
tected in the capillaries, or in the veins. This arises from 
several circumstances. One of them is that the capacity 
of the branches of an artery is greater than the capacity 
of its trunk, and the capacity of the capillaries, as a whole, 
is greater than that of all the small arteries put together. 
Hence, supposing the capacity of the trunk to be 10, that 
of its branches 50, and that of the capillaries into which 
these open 100, it is clear that a quantity of fluid thrown 
into the trunk, sufficient to dilate it by one-tenth, and to 
produce a very considerable and obvious effect, could not 
distend each branch by more than ^o^? an( ^ each capil- 
lary by y^o^th of its volume, an effect which might be quite 
imperceptible. 



WORKING OF THE HEART AND VESSELS. tfl 

But this is not all. Did the pulse merely become in- 
distinguishable on account of its division and dispersion 

among SO many capillaries, it ought to be felt again when 
the blood is once more gathered up into a few large venous 

trunks. But it is not. The pulse is definitely lost at the 
capillaries. There is, under ordinary circumstances, no 

pulse whatever in the veins, except sometimes a backward 
pulse from the heart along the great venous trunks ; but 
this is quite another matter. 

61. Cause of a Steady Capillary Flow. — This actual loss, 
or rather transformation of the pulse, is effected by means 
of the elasticity of the arterial walls, in the following man- 
ner : 

In the first place, it must be borne in mind that, owing 
to the minute size of the capillaries and small arteries, the 
amount of friction taking place in their channels when the 
blood i> passing through them is very great ; in other words, 
they offer a very great resistance to the passage of the 
blood. 

The consequence of this is, that the blood cannot get 
through the capillaries, in spite of the fact that their total 
area is so much greater than that of the aorta, into the 
veins so fast as it is throws into the arteries by the heart. 
The whole arterial system, therefore, becomes over -dis- 
tended with blood. 

Xow, we know by experiment that, under such condi- 
tions as these, an elastic tube has the power, if long enough 
and elastic enough, to change a jerked impulse into a con- 
tinuous flow. If a syringe (or one of the elastic bottles 
now so frequently in use) be fastened to one end of a long 

— tube, and water be pumped through the tube, it will 

v from the far end in jerks, corresponding to the jerks 
the syringe. This will be the case whether the tube be 

quite open at the far end. or drawn out to a line point so 

•i- t<. offer great resistance to the outflow of the water. 
The glass tube is a rigid tube, and there is no elasticity to 



62 ELEMENTARY PHYSIOLOGY. 

be brought into play. If now a long India-rubber tube be 
substituted for the glass tube, it will be found to act differ- 
ently, according as the opening at the far end is wide or 
narrow. 

If it is wide, the water flows out in jerks, nearly as dis- 
tinct as those from the glass tube. There is little resist- 
ance to the flow, little distention of the India-rubber tube, 
little elasticity brought into play. 

If, however, the opening be narrowed, as by fastening 
to it a stopcock or a glass tube drawn to a point, or if a 
piece of sponge be thrust into the end of the tube ; if, in 
fact, in an} 7 way resistance be offered to the outflow of the 
water, the tube becomes distended, its elasticity is brought 
into play, and the water flows out from the end, not in 
jerks but in a stream, which is more and more completely 
continuous the longer and more elastic the tube. 

Substitute for the syringe the heart, for the stopcock 
or sponge the capillaries and small arteries, for the India- 
rubber tube the whole arterial system, and you have ex- 
actly the same result in the living body. Through the 
action of the elastic arterial walls the separate jets from 
the heart are blended into one continuous stream. The 
whole force of each blow of the heart is not at once spent 
in driving a quantity of blood out of the capillaries ; a part 
only is thus spent, the rest goes to distend the elastic ar- 
teries. But, during the interval between that beat and 
the next, the distended arteries are narrowing again, by 
virtue of their elasticity, and so are pressing the blood on 
into the capillaries with as much force as they were them- 
selves distended by the heart. Then comes another beat, 
and the same process is repeated. At each stroke the 
elastic arteries shelter the capillaries from part of the sud- 
den blow, and then quietly and steadily pass on that part 
of the blow to the capillaries during the interval between 
the strokes. 

The larger the amount of elastic arterial wall thus 



WORKING OF THE HEART AND VESSELS. 

brought into play, i. e., the greater the distance from the 
heart, the greater is the fraction of each heart's stroke 
which is thus converted into a steady elastic pressure be- 
tween the beats. Thus the puke heroines less and I Sfl 
marked the farther you go from the heart; any given 
length of the arterial system, so to speak, being sheltered 

by the lengths between it and the heart. 

Every inch of the arterial system may, in fact, be con- 
sidered as converting a small fraction of the heart's j «rk 

into a steady pressure, and when all these fractions an 1 
summed tip together in the total length of the arterial 
system no trace of the jerk is left. 

A- the effect of each systole becomes diminished in the 
smaller vessels by the causes above mentioned, that of this 

-taut pressure becomes more obvious, and gives rise to 
a steady passage of the fluid from the arteries towards the 
veins. In this way. in fact, the arteries perform the same 
(unctions as the air-reservoir of a lire-engine, which oon- 

ts the jerking impulse given by the pumps into the 
ly flow of the delivery-hose. 

62. Velocity of the Blood Current— Such is the gen- 

! result of the mechanical conditions of the organs of 
the circulation combined with the rhythmical activity of 
the heart. This activity drives the fluid contained in 
these organs out of the heart into the arteries, thence to 
the capillaries, and from them through the veins back to 
the heart And, in the course of these operations, it gi 

. incidentally, to the beating of the heart, the sounds 
of the heart, and the pulse. 

It has been found, by experiment, that in the horse it 
takes about half a minute for any Bubstance, a-, for in- 
stance, a chemical body, whose presence in the blood can 

sily be recognized, to comple the circuit, ex. gr., to pass 

from the jugular rein down through the right side of the 
h^art, the lungs, the left side of the heart, up through t lie ar- 
teries of the head and neck, and so back to the jugular vein. 



64 ELEMENTARY PHYSIOLOGY. 

By far the greater portion of this half-minute is taken 
up by the passage through the capillaries, where the blood 
moves, it is estimated, at the rate only of about one and a 
half inch in a minute, whereas through the carotid artery 
of a dog it flies along at the rate of about ten inches in a 
second. 

Of course, to complete the circuit of the circulation, a 
blood-corpuscle need not have to go through so much as 
half of an inch of capillaries in either the lungs or any of 
the tissues of the body. 

Inasmuch as the force which drives the blood on is (put- 
ting the other comparatively slight helps on one side) the 
beat of the heart and that alone, however much it may be 
modified, as we have seen, in character, it is obvious that 
the velocity with which the blood moves must be greatest 
in the aorta and diminish towards the capillaries. 

For with each branching of the arteries the total area 
of the arterial system is increased, the total width of the 
capillary tubes, if they were all put together side by side, 
being very much greater than that of the aorta. Hence 
the blood, or a corpuscle, for instance, of the blood being 
driven by the same force, viz., the heart's beat, over the 
wmole body, must pass much more rapidly through the 
aorta than through the capillary system or any part of that 
system. 

It is not that the greater friction in any capillary 
causes the blood to flow more slowly there and there only. 
The resistance caused by the friction in the capillaries is 
thrown back upon the aorta, which indeed feels the resist- 
ance of the whole vascular system ; and it is this tctal 
resistance which has to be overcome by the heart before 
the blood can move on at all. 

The blood driven everywhere by the same force simply 
moves more and more slowly as it passes into w T ider and 
wider channels. When it is in the capillaries it is slowest; 
after escaping from the capillaries, as the veins unite into 



THE GENERAL CIRCULATION. 05 

larger and larger trunks, and hence as the total venous 
area is getting less and less, the blood moves again Paster 
and faster for just the same reason that in the arteries it 
moved slower and slower. 

A verv similar case is that o( a river widening out in a 
plain into a lake 1 and then contracting into a narrow stream 

tin. The water is driven by one force throughout (that 
oi gravity). The current is much slower in the lake than 
in the narrower river either before or behind. 

Section IV. — The General Circulation* 

63. The Course of the Circulation. — It is now neces- 
sarv to trace the exact course of the circulation as a whole. 
And we may conveniently commence with a portion of the 
blood contained at any moment in the right auricle. The 
contraction of the right auricle drives that fluid into the 
right ventricle; the ventricle then contracts and forces it 
into the pulmonary artery ; from hence it passes into the 
capillaries of the lungs. Leaving these, it returns by the 
four pulmonary veins to the left auricle ; and the contrac- 
tion of the left auricle drives it into the left ventricle. 

The systole of the left ventricle forces the blood into 
the aorta. The branches of the aorta convey it into all 
parts of the body except the lungs; and from the capil- 
laries of all these parts, except from those of the intestines 
and certain other viscera in the abdomen, it is conveyed, 
by vessels which gradually unite into larger and larger 
trunks, into either the superior or the inferior vena cava, 
which carry it to the right auricle once more. 

Hut the blood brought to the capillaries of the stomach 
and intestines, Bpleen, and pancreas, is gathered into veins 

which unite into a single trunk — the r< ,,<i i><>,1<i. The 

vena porta' distributes it- blood to the liver, mingling with 

that supplied to the capillaries of the same organ by the 

hepatic artery. From these capillaries it is conveyed by 

small veins, which unite into a large trunk — the hepatic 
5 



66 ELEMENTARY PHYSIOLOGY. 

vein, which opens into the inferior vena cava. The flow 
of the blood from the abdominal viscera, through the liver, 
to the hepatic vein, is called the portal circulation. 

The heart itself is supplied with blood by the two 
coronary arteries which spring from the root of the aorta 
just above two of the semilunar valves. The blood from 
the capillaries of the heart is carried back by the coronary 
vein, not to either vena cava, but to the right auricle. The 
opening of the coronary vein is protected by a valve, so 
as to prevent the right auricle from driving the venous 
blood which it contains back into the vessels of the heart. 

64, Routes of the Travelling Blood-Particles. — Thus, the 
shortest possible course which any particle of the blood can 
take, in order to pass from one side of the heart to the 
other, is to leave the aorta by one of the coronary arteries, 
and return to the right auricle by the coronary vein. And, 
in order to pass through the greatest possible number of 
capillaries and return to the point from which it started, a 
particle of blood must leave the heart by the aorta and 
traverse the arteries which supply the alimentary canal, 
spleen, and pancreas. It then enters, firstly, the capil- 
laries of these organs ; secondly, the capillaries of the 
liver ; and, thirdly, after passing through the right side of 
the heart, the capillaries of the lungs, from which it re- 
turns to the left side and eventually to the aorta. 

Furthermore, from what has been said respecting the 
lymphatic system, it follows that any particle of matter 
which enters a lacteal of the intestine, will reach the right 
auricle by the superior cava, after passing through the 
lymph capillaries and channels of sundry lymphatic glands ; 
while any thing which enters the adjacent blood-capillary 
in the wall of the intestine will reach the right auricle by 
the inferior cava, after passing through the blood-capil- 
laries of the liver. 

65. Nervous Control of the Circulation. — It has been 
shown above (40) that the small arteries may be directly 



THE GENERAL CIRCULATION. G7 

affected by the nervous system, which controls the state 
of contraction of their muscular walls, and so regulates 
their calibre. The effect of this power of the nervous sys- 
tem LS to give it a certain control over the circulation in 
particular spot-, and t-> produce such a state of affairs 
that, although the force of the heart and the general con- 
dition of the vessels remain the same, the state of the cir- 
culation may he very different in different localities, 

66, Explanation of Blushing. — Blushing is a purely 
local modification of the circulation of this kind, antl it will 
be instructive to consider how a blush is brought about. 
An emotion — sometimes pleasurable, sometimes painful — 
takes possession of the mind: thereupon a hoi flush is felt, 
the >kin grows red, and, according to the intensity of the 
emotion, these changes are confined to the cheeks only, or 

•id to the M loots o{ the hair," or " all over." 

What is the cause of these changes? The blood is a 
: and a hot fluid ; the skin reddens. and grows hot, be- 
cause it- vessels contain an increased quantity of this red 
and hot fluid : and its vessels contain more, because the 
Bmall arteries suddenly dilate, the natural moderate con- 
traction of their muscles being superseded by a state of 
relaxation. In other words, the action of the nerves which 
cause this muscular contraction is suspended. 

On the other hand, in many people, extreme terror 
causes the skin to grow cold, and the face to appear pah- 
am! pinched. tinder these circumstances, in fact, the 
supply of blood to the skin is greatly diminished, in cou- 
[uence of an excessive stimulation of the nerves of the 
Small arteries, which causes them to contract and so to cul 
Off the Supply of blood more or less completely. 

67. Experimental Proof of this. — That this is the real 

te of the case may be proved experimentally upon rab- 
bit-. These animals may be made to blush artificially. If, 

in a rabbit, the sympathetic nerve, which Sends branches 
to the ve88els of the head, is cut, the ear of" the rabbit, 



68 ELEMENTARY PHYSIOLOGY. 

which is covered by so delicate an integument that the 
changes in the vessels can be readily perceived, at once 
blushes. That is to say, the vessels dilate, fill with blood, 
and the ear becomes red and hot. The reason of this is, 
that when the sympathetic is cut, the nervous stimulus 
which is ordinarily sent along its branches is interrupted, 
and the muscles of the small vessels, which were slightly 
contracted, become .altogether relaxed. 

And now it is quite possible to produce pallor and cold 
in the rabbit's ear. To do this it is only necessary to irri- 
tate the cut end of the sympathetic which remains con- 
nected w^ith the vessels. The nerve then becomes excited, 
so that the muscular fibres of the vessels are thrown into a 
violent state of contraction, which diminishes their calibre 
so much that the blood can hardly make its way through 
them. Consequently, the ear becomes pale and cold. 

68. Relation of this Nervous Control to Disease. — The 
practical importance of this local control exerted by the 
nervous system is immense. When exposure to cold gives 
a man catarrh, or inflammation of the lungs, or diarrhoea, 
or some still more serious affection of the abdominal vis- 
cera, the disease is brought about through the nervous 
system. The impression made by the cold on the skin is 
conveyed to the nervous centres, and so influences the vaso- 
motor nerves (as the nerves which govern the walls of the 
vessels are called) of the organ affected as to cause their 
partial paralysis, and produce that state of congestion (or 
undue distention of the vessels) which so commonly ends 
in inflammation. (See 327.) 

69. Nervous Control over the Heart. — Is the heart, in 
like manner, under the contol of the central nervous system ? 

As we all know, it is not under the direct influence of 
the will, but every one is no less familiar with the fact that 
the actions of the heart are wonderfully affected by all 
forms of emotion. Men and women often faint, and have 
sometimes been killed by sudden and violent joy or sor- 



THE GENERAL CIRCULATION. 69 

row; and, when they taint or die in this way, they do so 
because the perturbation of the brain gives rise to a some- 
thing which arrests the heart as dead as you stop a stop- 
watch with a spring. On the 4 other hand, other emotions 
cause that extreme rapidity and violence of action which 
we call palpitation. 

Now, there are three sets o( nerves in the heart : one 
are supplied by ganglia^ or masses of nerve-cells, in its 
substance; another set come from the sympathetic nerve; 
a third set are branches of a remarkable nerve, which pro- 
Is straight from the brain, and is called the pneumo- 
Uric nerve. There is every reason to believe that the 
ular rhythmical succession of the ordinary contractions 
of the heart depends upon the ganglia lodged in its sub- 
ice. At any rate, it is certain that these movements 
depend neither on the sympathetic, nor on the pneumo- 
• they go "ii as well when the heart is removed 
from the body. 

In tlte next place, there is much reason to believe that 
the influence which increases the rapidity of the heart's 
action i^ exerted through the sympathetic. 

And, lastly, it is quite certain that the influence which 
ftffests the heart's action is supplied by the pnenmogastric. 
This may be demonstrated in animals, such as frogs, with 

70. The Circulation directly observed. — If a frog be 

pithed, or its brain destroyed, so as to obliterate 4 all sensi- 
bility, the animal will continue to live, and its circulation 
will go on perfectly well for an indefinite period. The body 

maybe laid open without causing pain or other disturb- 
ance, and then the heart will be observed beating with 

great regularity. It is possible to make the heart move a 

long index backwards and forwards; and if frog and index 

are covered with a glass shade, the -<i'w under which is kepi 
moist, the index will vibrate with great steadiness for a 
couple of days. 



10 



ELEMENTAEY PHYSIOLOGY. 



It is easy to adjust to the frog thus prepared a contriv- 
ance by which electrical shocks may be sent through the 
pneumogastric nerves, so as to irritate them. The moment 




Portion of the web of a frog's foot seen under a 1<~>v magnifying power, the blood-ves- 
sels only being- represented except in the corner of the field, where in the portion 
marked oif the pigment spots are also drawn. 

a., small arteries ; «., small veins: the minute tubes joining the rrteries and the veins 
are the capillaries. The arrows denote the direction of the circulation. The larger 
artery running straight up in the middle line breaks up into capillaries at points higher 
up than can be shown in the drawing. 



this is done the index stops dead, and the heart will be 
found quiescent, with relaxed and distended walls. After 
a little time the influence of the pneumogastric passes off 7 



THE GENERAL CIRCULATION. 71 

the heart recommences its work as vigorously as before, 
and the index vibrates through tin* same arc as formerly. 
With careful management, this experiment may he re- 
peated very many times; and, alter every arrest by the 
irritation of the pneumogastric, the heart resumes its work. 

71. Proof of the Circulation in Man. — The evidence 
that the blood circulates in man, although perfectly conclu- 
sive, is almost all indirect. The most important jxnnts in 
i he evidence are as follows : 

In tin 1 first place, the disposition and structure of the 
_ ins {)( circulation, and more especially the arrangement 
of tlit- various valves, will not, as was shown by Harvey, 
permit the blood to Bow in any other direction than in the 
i^M- described above. Moreover, we can easily with a 
syringe inject a fluid from the vena cava, for instance, 
through the right side of the heart, the lungs, the left side 

the heart, the arteries, and capillaries, back to tin 1 vena 
Cava : but not the other way. In the second place, we 
know that in the living body tin 1 blood is continually flow- 
ing in the arteries towards the capillaries, because when 
an artery is tied, in a living body, it swells up and pulsate- 
on the side of the ligature nearest the heart, whereas on 
the other side it becomes empty, and the tissues supplied 
by the artery become pale from the want of a supplv of 
blood to their capillaries. And when we cut an artery the 
blood is pumped out in jerks from the cut end nearest the 

it, whereas little or no blood comes from the other end. 
When, however, we tie a vein the state of things is re- 
versed, the swelling taking place on the side farthest from 
the heart, etc., etc., showing that in the veins the bio 1 

flows from the capillaries to the heart. 

But certain of the lower animals, the whole, or parts, 

of the body of whi.-h are transparent, readily afford direct 
proof of the circulation, the blood visibly rushing from the 
arterie> into the capillaries, and from the capillaries into 

the vein-. BO long as the animal 18 alive and it> heart is at 



72 



ELEMENTARY PHYSIOLOGY. 



work. The animal in which the circulation can be most 
conveniently observed is the frog. The web between its 




Fig. 19. 
Very Small Portion of Fig. 18, very highly magnified. 
A., walls of capillaries ; B., tissue of web lying" between the capillaries; (7., cells of 
epilermis covering web (these are only shown in the right-hand and lower part of the 
field ; in the other parts of the field the focus of the microscope lies below the epider- 
mis) ; Z>., nuclei of these epidermic cells ; E., pigment-cells contracted, not partially- 
expanded as in Fig. 18; F., red blood-corpuscle (oval in the frog) passing along capil- 
lary—nucleus not visible; G., another corpuscle squeezing its way through a capillary, 
the canal of which is smaller than its own transverse diameter; If., another bending 1 as 
it slides round a corner; K., corpuscle in capillary seen through the epidermis; Z, 
white blood-corpuscle. 



THE MICROSCOPIC ELEMENTS OF THE BLOOD. 

is very transparent, and the particles suspended in its 
blood are so large thai they can be readily seen as they 
dip swiftly along with the stream of blood, when the toes 
are fastened out, and the intervening web is examined 

under even a low magnifying power (Figs, 18 and 19). 



CHAPTER III. 

THE BLOOD AND THE LYMPH. 

Si now I. — The Microscopical Elements of tin Blood. 

72. How to examine it. — In order tc become properly 
acquainted with the characters of the blood, it is necessary 
t<> examine it with a microscope magnifying at least three 

or four hundred diameters. Provided with this instrument, 
a hand-lens, and BOme slips of thick and thin glass, the stu- 
dent will be enabled to follow the present chapter. 

The most convenient mode of obtaining small quantities 
of blood for examination is to twist a piece of string, pretty 
tightly, round the middle of the last joint of the middle, or 
ling-finger, of the loft hand. The end of the finger will 
immediately swell a little, and become darker colored, in 
consequence of the obstruction to the return of the blood 
in the veins caused by the ligature. When in this con- 
dition, if it be slightly pricked with a sharp clean needle 

Operation which causes hardly any pain), a good-sized 
drop of blood will at one- exude. Let it be deposited on 

■ of the >lip< of thick glass, and covered lightly and 
gently with a piece of the thin glass, bo as to spread it out 

:ily into a thin layer. Le1 8 second slide receive an- 
other drop, and. to keep it from drying, let it be put under 

an inverted watch-glass or wine-glass, with a bit of wet 
blotting-paper inside Lei a third drop be deal! with in 



74 ELEMENTARY PHYSIOLOGY. 

the same way, a few granules of common salt being first 
added to the drop. 

73. Its Appearance when magnified. — To the naked eye 
the layer of blood upon the first slide will appear of a pale- 
reddish color, and quite clear and homogeneous. But on 
viewing it with even a pocket-lens its apparent homo- 
geneity will disappear, and it will look like a mixture of 
excessively fine yellowish-red particles, like sand, or dust, 
with a watery, almost colorless, fluid. Immediately after 
the blood is drawn, the particles will appear to be scat- 
tered very evenly through the fluid, but by degrees they 
aggregate into minute patches, and the layer of blood be- 
comes more or less spotty. 

The " particles " are what are termed the corpuscles of 
the blood ; the nearly colorless fluid in which they are sus- 
pended is the plasma. 

The second slide may now be examined. The drop of 
blood will be unaltered in form, and may perhaps seem to 
have undergone no change. But, if the slide be inclined, 
it will be found that the drop no longer flows ; and, indeed, 
the slide may be inverted without the disturbance of the 
drop, which has become solidified, and may be removed, 
with the point of a penknife, as a gelatinous mass. The 
mass is quite soft and moist, so that this setting, or coagu- 
lation^ of a drop of blood is something very different from 
its drying. 

On the third slide, this process of coagulation will be 
found not to have taken place, the blood remaining as fluid 
as it was when it left the body. The salt, therefore, has 
prevented the coagulation of the blood. Thus this very 
simple investigation teaches that blood is composed of a 
nearly colorless plasma, in which many colored corpuscles 
<re suspended ; that it has a remarkable power of coagu- 
lating ; and that this coagulation may be prevented by ar- 
tificial means, such as the addition of salt. 

74, The Blood-Corpuscles. — If, instead of using the hand 



THE MICROSCOPIC ELEMENTS OF THE BLOOD. 



75 



lens, the drop of blood on the first slide be placed under 
the microscope, the particles, or corpuscles, of the blood 
will be found to be bodies with very definite characters, 
and of two kinds, called respectively the red corpuscles and 
the colorless corpuscles. The former are much more numer- 
ous than the latter, and have a yellowish-red tinge; while 
the latter, somewhat larger than the red corpuscles, are, as 
their name implies, pale and devoid of coloration. 

75. Their Size, Form, and Appearance. — The corpus- 
cles differ also in other and more important respects. The 
Ted corpuscles (Fig. '20) are flattened circular disks, on an 




Vl,. 20. 

wit Winn: Cobfi ras Blood magnified. 

A. Moderately magnified. The red lying in rouleaux; .-it a 

d two white corpc 
/>. Bed corpuscles much more highly m ignifled. Been in face; < '.. ditto, seen in pro- 
file: . rouleaux, rather more highlj ; /•/.. ;i red corpuscle swollen 
sphere by ImbfWtiori of water. 
F. \ white corpuscle magafl I, . G.. ditto throwing out some blunt 
A., ditto, treated with acetic add, and showing nucieui magnifled same 
at i> 

<L !:• d - oq o\, r . 

/ D only. 



76 ELEMENTARY PHYSIOLOGY. 

average -g-^^th of an inch in diameter, and having about 
one-fourth of that thickness. It follows that rather more 
than ten millions of them will lie on a space one inch square, 
and that the volume of each corpuscle does not exceed 

120 0oWoOQ tb ° f a CubiG iDCn - 

The broad faces of the disks are not flat, but somewhat 
concave, as if they were pushed in towards one another. 
Hence the corpuscle is thinner in the middle than at the 
edges, and when viewed under the microscope, by trans- 
mitted light, looks clear in the middle and darker at the 
edges, or dark in the middle and clear at the edges, ac- 
cording to circumstances. When, on the other hand, the 
disks roll over and present their edges to the eye, they 
look like rods. All these varieties of appearance may be 
made intelligible by turning a round biscuit or muffin, 
bodies similar in shape to the red corpuscles, in various 
ways before the eye. 

76. Structure and Changes of Form. — The red corpus- 
cles are very soft, flexible, and elastic bodies, so that they 
readily squeeze through apertures and passages narrower 
than their own diameters, and immediately resume their 
proper shapes (Fig. 19, G.H.). The exterior of each cor- 
puscle is denser than its interior, which contains a semi- 
fluid, or quite fluid matter, of a red color, called haemoglo- 
bin. By proper processes this may be resolved into an 
albuminous substance sometimes called globulin, and a 
peculiar coloring matter, which is called hcematm. The 
interior substance presents no distinct structure. 

From the density of the outer as compared with the 
inner substance of each corpuscle, they are, practically, 
small flattened bags, or sacs, the form of which may be 
changed by altering the density of the plasma. Thus, if it 
be made denser by dissolving saline substances, or sugar, 
in it, water is drawn from the contents of the corpuscle to 
the dense plasma, and the corpuscle becomes still more 
flattened, and very often much wrinkled. On the other 



THE MICROSCOPIC ELEMENTS OF TIIK BLOOD. 77 

hand, if the plasma be diluted with water, the latter forces 
itself into and dilutes the contents of the corpuscle, causing 
the latter to swell out, and even become spherical ; and, 
by adding dense and weak solutions alternately, the cor- 
puscles may he made to become successively spheroidal 

and discoidal. Exposure to carhonic-acid u'as seems to 
Cause the corpuscles to swell out ; oxygen gas, on the con- 
trary, appears to flatten them. 

77. The Colorless Corpuscles. — The color!*** corpuscles 
(Fig, 20, a '/., F.ir.K.) are larger than the red corpuscles, 
their average diameter being ^-sWtli of an inch. They are 
further seen, at a glance, to differ from the red corpuscles 
by the extreme irregularity of their form, and by their 
tendency to attach themselves to the glass slide, while 
the red corpuscles iloat about and tumble freely over one 
another. 

A still more remarkable feature of the colorless cor- 
puscles than the irregularity of their form is the unceasing 

A 







b c d e 

J-'i... 21. 

Buoanara Fiona lmumbd bi Colorless Cobppsclbs of IItman Blood. 
(Magnified about sis hundred diameters.) 

Th.- interval between the forms <>. '>. ,-. ,/. was a minute; between <l and e two 
minutes; so that the whole series of changes from a to e took five minutes. 



variation of shape which they exhibit. The form of a red 
corpuscle is changed only by influences from without, such 
as pressure, or the like ; tint of the colorless corpuscle is 
undergoing constanl alteration, as the result of changes 
taking place in its own substance. To see these changes 
well, a microscope, with a magnifying power of five or six 
hundred diameters, is requisite : and, even then, they are so 
gradual that the best way to ascertain their existence is tc 



78 ELEMENTARY PHYSIOLOGY. 

make a drawing of a given colorless corpuscle at intervals 
of a minute or two. This is w T hat has been done with the 
corpuscle represented in Fig. 21, in which a represents the 
form of the corpuscle when first observed ; 5, its form a 
minute afterwards; c, that at the end of the second; d, 
that at the end of the third ; and 6, that at the end of the 
fifth minute. 

Careful watching of a^ colorless corpuscle, in fact, shows 
that every part of its surface is constantly changing — un- 
dergoing active contraction, or being passively dilated by 
the contraction of other parts. It exhibits contractility in 
its lowest and most primitive form. 

78. Structure and Contractility.— While they are thus 
living and active, no correct notion can be formed of the 
structure of the colorless corpuscles. By diluting the blood 
with water, or, still better, with water acidulated with 
acetic acid, the corpuscles are killed, and become dis- 
tended, so that their real nature is shown. They are then 
seen to be spheroidal bags, or sacs, with very thin walls ; 
and to contain in their interior a fluid which is either 
clear or granular, together with a spheroidal vesicular 
body, which is called the nucleus (Fig. 20, K). It some- 
times, though very rarely, happens that the nucleus has a 
red tint. 

The sac-like colorless corpuscle, with its nucleus, is 
what is called a nucleated cell. It will be observed that it 
lives in a free state in the plasma of the blood, and that it 
exhibits an independent contractility. In fact, except that 
it is dependent for the conditions of its existence upon the 
plasma, it might be compared to one of those simple or- 
ganisms which are met with in stagnant water, and are 
called Amoebae. 

79. Derivation of the Corpuscles. — That the red corpus- 
cles are in some way or other derived from the colorless 
corpuscles may be regarded as certain : but the steps of 
4ie process have not been made out with perfect certainty. 



THE MICROSCOPIC ELEMENTS OF THE BLOOD. 79 

There is very great reason, however, for believing that the 
red corpuscle is simply the nucleus of the eolorless cor- 
puscle somewhat enlarged; flattened from side to side; 
changed, by development within its interior of a red color- 
ing-matter ; and set free by the bursting of the sac or wall 
of the colorless corpuscle. In other words, the red corpus- 
( le is a free nucleus. 

The origin of the colorless corpuscles themselves is not 
certainly determined; but it is highly probable that they 
are constituent cells of particular parts of the solid sub- 
stance of the body which have been detached and carried 
into the blood, and that this process is chiefly effected in 
what are called the ductless gland* (see 155), from whence 
the detached cells pass, as lymph-corpuscles, directly, or 
indirectly, into the blood. 

Tin 1 following facts are of importance in their bearing 
on the relation between the different kinds of corpuscles : 

(a) The invertebrate animals, 1 which have true blood- 
OOrpuscles, possess only such as resemble the colorless cor- 
puscles of man. 

(/>) The lowest vertebrate animal, the lancelot (Arnphi- 
oxus), possesses only colorless corpuscles; and the very 
young embryos 2 of all vertebrate animals have only color- 
less and nucleated corpuscles. 

(') All the vertebrated animals, the young of which are 
born from r^<x>. 3 have 1 two kinds of corpuscles — colorless 
corpuscles, like those of man, and large red-colored cor- 
puscles, which are generally oval, and further differ from 
those of man in presenting a nucleus. In fact, they are 
simply the colorless corpuscles enlarged and colored. 

('/» All animals which suckle their young (or what are 
called mammals) have, like man, two kinds of corpuscles J 

1 Invertebrate intmahi ere anhnah devoid of backbones, snob a^ Insects, snails, 

8ea-an«Tn<. rtebrate animal- ire DShea, amphibia, reptiles, t>inl>. and mam 

tfae ru dim e n tary unborn young of any creature. 
* '1 :. mpnlbfa, reptilea, and birds 



80 ELEMENTARY PHYSIOLOGY. 

colorless ones, and small colored corpuscles — the latter 
being always flattened, and devoid of any nucleus. They 
are usually circular, but in the camel tribe they are ellip- 
tical. And it is worthy of remark that, in these animals, 
the nuclei of the colorless corpuscles become elliptical. 

(e) The colorless corpuscles differ much less from one 
another in size and form, in the vertebrate series, than the 
colored. The latter are. smallest in the little musk-deer, 
in which animal they are about a quarter as large as those 
of a man. On the other hand, the red corpuscles are 
largest in the Amphibia (or frogs and salamanders), in 
some of which animals they are ten times as long as in 
man. 

80. Changes attending the Death of the Blood. — As the 
blood dies, its several constituents, w^hich have now been 
described, undergo marked changes. 

The colorless corpuscles lose their contractility, but 
otherwise undergo little alteration. They tend to cohere 
neither with one another, nor with the red corpuscles, but 
adhere to the glass plate on which they are placed. 

It is quite otherwise with the red corpuscles, w T hich at 
first, as has been said, float about and roll, or slide, over 
each other quite freely. After a short time (the length of 
which varies in different persons, but usually amounts to 
two or three minutes), they seem, as it were, to become 
sticky, and tend to cohere ; and this tendency increases 
until, at length, the great majority of them become ap- 
plied face to face, so as to form long series, like rolls of 
coin. The end of one roll cohering with the sides of an- 
other, a net-work of various degrees of closeness is pro- 
duced (Fig. 20, A.). 

The corpuscles remain thus coherent for a certain length 
of time, but eventually separate, and float freely again. The 
addition of a little water, or dilute acids or saline solu- 
tions, will at once cause the rolls to break up. 

It is from this running of the corpuscles together into 



PROPERTIES OF THE BLOOD. 81 

patches of not-work thai the change noted above in the 
appearances of the layer of blood, viewed with a lens, 
arises. So long as the corpuscles are separate, the sandy 
appearance lasts; but when they run together, the layer 
appears patchy or spotted. 

The red corpuscles rarely, if ever, all run together into 
rolls, some always remaining free in the meshes of the net. 
In contact with air, or if subjected to pressure, many of 
the red corpuscles become covered with little knobs, so as 
to look like minute mulberries — an appearance which has 
been mistaken for a breaking up, or spontaneous division, 
of the corpuscles (Fig. 20, U.K.). 

81. Blood-Crystals. — There is a still more remarkable 
change which the red blood - corpuscles occasionally un- 
dergo. Under certain circumstances, the peculiar red sub- 
stance which forms the chief mass of their contents, and 
which has been called haemoglobin (from its readily break- 
ing up into globulin and luematin, 76), separates in a crys- 
talline form. In man, these crystals have the shape of 
prisms; in other animals they take other forms. Human 
blood crystallizes with difficulty, but that of the Guinea- 
pig, rat, or dog, much more easily. The best way to see 
these Mood-crystals is to take a little rat's blood, from 
which the fibrin has been removed, shake it up with a 
little ether, and let it stand in the cold for some hours. A 
sediment will form at the bottom, which, when examined 
with the microscope, will be found to consist of long, nar- 
row crystals. Crystallization is much assisted by adding 

: the ether a small quantity of alcohol. 

Section II. — Properties of the Blood. 

82. Its Coagulation. — When the layer of blood has been 

drawn ten or fifteen minutes, the plasma will be seen to be 
no longer clear. It then exhibits multitudes of extremely 
delicate filaments of a Bubstance called Fibrin^ which have 
been deposited from it, and which traverse it in all direo- 

6 



82 ELEMENTARY PHYSIOLOGY. 

tions, uniting with one another and with the corpuscles, 
and Tending the whole into a semi-solid mass. 

It is this deposition of fibrin which is the cause of the 
apparent solidification, or coagulation, of the drop upon 
the second slide ; but the phenomena of coagulation, 
which are of very great importance, cannot be properly 
understood until the behavior of the blood, when drawn in 
larger quantity than a drop; has been studied. 

83. Separation of its Constituents. — When, by the or- 
dinary process of opening a vein with a lancet, a quantity 
of blood is collected into a basin, it is at first perfectly 
fluid : but in a very few minutes it becomes, through 
coagulation, a jelly-like mass, so solid that the basin may 
be turned upside-down without any of the blood being 
spilt. At first the clot is a uniform red jelly, but very 
soon drops of a clear, yellowish, w^atery-looking fluid make 
their appearance on the surface of the clot, and on the 
sides of the basin. These drops increase in number, and 
run together, and after a while it has become apparent 
that the originally uniform jelly has separated into two 
very different constituents — the one a clear, yellowish 
liquid ; the other a red, semi-solid mass, which lies in the 
liquid, and at the surface is paler in color and firmer than 
in its deeper part. 

The liquid is called the serum / the semi-solid mass the 
clot, or crassamentum. Now, the clot obviously contains 
the corpuscles of the blood, bound together by some other 
substance ; and this last, if a small part of the clot be ex- 
amined microscopically, will be found to be that fibrous- 
looking matter, fibrin, which has been seen forming in the 
thin layer of blood. Thus the clot is equivalent to the cor- 
puscles plus the fibrin of the plasma, while the serum is 
the plasma minus the fibrinous elements which it con- 
tained. 

84. The Bufly-Coat.— The corpuscles of the blood are 
slightly heavier than the plasma, and therefore, when the 



PROPERTIES OF THE BLOOD. 83 

blood is drawn, they sink very slowly towards the bottom. 
Hence the upper part of the clot contains fewer corpuscles, 
and is lighter in color, than the lower part — there being 
fewer corpuscles left in the upper layer of plasma for the 
fibrin to catch when it sets. And there arc some condi- 
tions of the blood in which the corpuscles run together 
much more rapidly and in denser masses than usual. 
Hence they more readily overcome the resistance of the 
plasma to their falling, just as feathers stuck together in 
masses fall much more rapidly through the air than the 
same feathers when loose. When this is the case, the 
upper stratum o( plasma is quite free from red corpuscles 
before the fibrin forms in it ; and, consequently, the upper- 
most layer of the clot is nearly white: it receives the name 
o( the buffy-coat. 

After the clot is formed, the fibrin shrinks and squeezes 
out much of the serum contained within its meshes; and, 
other things being equal, it contracts the more the fewer 
corpuscles there are in the way of its shrinking. Hence, 
when the buffy-coat is formed, it usually contracts so much 
i give the clot a cup-like upper surface. 

Thus the bufiy-coat is fibrin naturally separated from 
rhe red corpuscles; the same separation maybe effected, 
artificially, by whipping the blood with twigs as soon as it 
IS drawn, until its coagulation is complete. Under these 
circumstances the fibrin will collect upon the twigs, and a 
red fluid will be left behind, consisting of the serum plus 
the red corpuscles, and many of the colorless ones. 

85. Conditions influencing Coagulation. — The coagula- 
tion of the blood i- hastened, retarded, or temporarily pre- 
vented, by many circumstances. 

(a) Temperatur . — A high temperature accelerates the 

filiation of the blood; a low one retards it very greatly; 
and sun!' experimenters have stated that, when kept at a 
sufficiently low temperature, it does not coagulate at all. 

{b\ The Addition of SolubU Matter to the Blood. — Many 



84 ELEMENTARY PHYSIOLOGY. 

saline substances, and more especially sulphate of soda and 
common salt, dissolved in the blood in sufficient quantity, 
preyent its coagulation ; but coagulation sets in when 
water is added, so as to dilute the saline solution. 

(c) Contact vnth Living or not Living Matter, — Contact 
with not living matter promotes the coagulation of the 
blood. Thus, blood drawn into a basin begins to coagu- 
late first where it is in contact with the sides of the basin j 
and a wire introduced into a living vein will become coated 
with fibrin, although perfectly fluid blood surrounds it. 

On the other hand, direct contact with living matter re- 
tards, or altogether prevents, the coagulation of the blood. 
Thus blood remains fluid for a very long time in a portion 
of a vein which is tied at each end. 

The heart of a turtle remains alive for a lengthened pe- 
riod (many hours or even days) after it is extracted from 
the body ; and, so long as it remains alive, the blood con- 
tained in it will not coagulate, though, if a portion of the 
same blood be removed from the heart, it will coagulate in 
a few r minutes. 

Blood taken from the body of the turtle, and kept from 
coagulating by cold for some time, may be poured into the 
separated, but still living, heart, and then w 7 ill not coagulate 

Freshly-deposited fibrin acts somewhat like living mat- 
ter, coagulable blood remaining fluid for a long time in 
tubes coated with such fibrin. 

86. Nature of the Process of Coagulation. — The coagu- 
lation of the blood is an altogether physico chemical pro- 
cess, dependent upon the properties of certain of the con- 
stituents of the plasma, apart from the vitality of that fluid. 
This is proved by the fact that if blood-plasma be prevented 
from coagulating by cold, and greatly diluted, a current of 
carbonic acid passed through it will throw down a white 
powdery substance. If this white substance be dissolved 
in a weak solution of common salt, or in an extremely w 7 eak 
solution of potash or soda, it ; after a w 7 hile, coagulates, and 



PROPERTIES OP THE BLOOD. 85 

a it-Ids a clot of true pure fibrin. It would be absurd 10 sup- 
pose that a substance which has been precipitated from its 

solution, and redissolved, still remains alive. 

There are reasons for believing that this white sub- 
stance consists of two constituents of very similar compo- 
sition, which exist separately in living blood, and the 
union of which is the cause of the act of coagulation. 
These reasons may be briefly stated thus: The pericar- 
dium and other serous cavities in the body contain a clear 
fluid, which has exuded from the blood-vessels, and con- 
tains the elements of the bipod without the blood-corpus- 
cles. This fluid sometimes coagulates spontaneously, as 
the blood-plasma would do, but very often shows no dis- 
position to spontaneous coagulation. When this is the 
, it may nevertheless be made to coagulate, and yield 
a true fibrinous clot, by adding to it a little serum of blood. 
\, if -.rum of blood be largely diluted with w^ater, 
and a current of carbonic-acid gas be passed through it, a 
white powdery substance will be thrown down; this, re- 
solved in a dilute saline, or extremely dilute alkaline 
solution, will, when added to the pericardial fluid, produce 
n as good a clot as that obtained with the original 
in. 

This white substance has been called globulin. It ex- 
ists not only in serum, but also, though in smaller quan- 
tities, in connective tissue, in the cornea, in the humors of 
the eye, and in some other fluids of the body. 

It possesses the same general chemical properties as 
the albuminous substance which enters so largely into the 
the Composition of the red corpuscles (76), and hence, at 

present, bears the same name. But when treated with 
chemical reagents, even with such as do not produce any 
appreciable effect on its chemical composition, it very 

Speedily loses its peculiar power of causing serous fluids 

to coagulate. For instance, this power is destroyed by an 

\l alkali, or by the presence of acids. 



86 ELEMENTARY PHYSIOLOGY. 

Hence, though there is great reason to believe that the 
fibrino-plastie globulin (as it has been called) which exists 
in serum does really come from the red corpuscles, the 
globulin which is obtained in large quantities from these 
bodies, by the use of powerful reagents, has no coagulat- 
ing effect at all on pericardial or other serous fluids. 

Though globulin is so susceptible of change when in 
solution, it may be dried at a low temperature and kept in 
the form of powder for many months, without losing its 
coagulating power. 

Thus globulin, added, under proper conditions, to serous 
effusion, is a coagulator of that effusion, giving rise to the 
development of fibrin in it. 

It does so by its interaction with a substance contained 
in the serous effusion, which can be extracted by itself, and 
then plays just the same part towards a solution of globu- 
lin, as globulin does towards its solution. This substance 
has been called fibrinogen. It is exceedingly like globu- 
lin, and may be thrown down from serous exudation by 
carbonic acid, just as globulin may be precipitated from 
the serum of the blood. When redissoived in an alkaline 
solution, and added to any fluid containing globulin, it acts 
as a coagulator of that fluid, and gives rise to the develop- 
ment of a clot of fibrin in it. In accordance with what has 
just been stated, serum of blood which has completely 
coagulated may be kept in one vessel, and pericardial fluid 
in another, for an indefinite period 5 if spontaneous decom- 
position be prevented, without the coagulation of either. 
But let them be mixed, and coagulation sets in. 

Thus it seems to be clear, that the coagulation of the 
blood, and the formation of fibrin, are caused primarily by 
the interaction of two substances (or two modifications of 
the same substance), globulin or fibrinoplastin and fibrino- 
gen, the former of which may be obtained from the serum 
of the blood, and from some tissues of the body ; while 
the latter is known, at present, only in the plasma of the 



PROPERTIES OF THE BLOOD. ST 

blood, of the lymph, and of the chyle, and in fluids derived 
from them. 

87. The Physical Qualities of the Blood.— The proverb 
that k * blood is thioker than water^' is literally true, as the 
bio (I is not only "thickened" by the corpuscles, of which 
it has been calculated thai do fewer than : 0.000,000,000 
(eighty times the number o( the human population of the 

>be) arc contained in a cubic inch, but is rendered slightly 
viscid by the solid matters dissolved in the plasma. The 
blood i> thus rendered heavier than water, its specific grav- 
ity being about L055. In other words, twenty cubic inches 
of blood have about the same weight as twenty-one cubic 

inches of water. 

The corpuscles are heavier than the plasma, and their 
volume is usually somewhat less than that of the plasma. 
Of colorless corpuscles there are usually not more than 
three or four for every thousand of red corpuscles; but the 
number varies very much, increasing shortly after food is 
taken, and diminishing in the intervals between meals. 

The blood is hot, its temperature being about 100° 

Fahr. 

88. The Chemical Composition of the Blood. — Consid- 
ered chemically, the blood is an alkaline fluid, consisting 

of water, of solid and of gaseous matters. 

The proportions of these several constituents vary ac- 
cording to age, sex, and condition, but the following state- 
ment holds good on the average: 

In every LOO parts of the blood there are 79 parts of 

water and 21 parts of dry solids; in other words, the water 

and the solids of the blood stand to one another in about 

the same proport ion as the nit rogen and the oxygen of t he 

Roughly -peaking, one-(juarter of the blood is dry, 

solid matter; three-quarters water. Of the 21 parts of dry 

solid-, 12 (= Iths) belong to the corpuscles The remain- 
in ir 9 are about two-third- («;.T parts = | ths) albumen (a 
Substance like white of egg, coagulating by heat), and 



88 ELEMENTARY PHYSIOLOGY. 

one-third (= -^th of the whole solid matter) a mixture of 
saline, fatty, and saccharine matters, sundry products of 
the waste of the body, and fibrin. The quantity of the 
latter constituent is remarkably small in relation to the 
conspicuous part it plays in the act of coagulation. Healthy 
blood, in fact, yields in coagulating not more than from 
two to four parts in a thousand of its weight of fibrin. 

The total quantity of gaseous matter contained in the 
blood is equal to rather less than half the volume of the 
blood; that is to say, 100 cubic inches of blood will contain 
rather less than 50 cubic inches of gases. These gaseous 
matters are carbonic acid, oxygen, and nitrogen; or, in 
other words, the same gases as those w T hich exist in the 
atmosphere, but in totally different proportions ; for where- 
as air contains nearly three-fourths nitrogen, one fourth 
oxygen, and a mere trace of carbonic acid, the average 
composition of the blood gases is nearly two-thirds car- 
bonic acid, rather less than one-third oxygen, and not one- 
tenth nitrogen. 

It is important to observe that blood contains much 
mere oxygen gas than could be held in solution by pure 
water at the same temperature and pressure. This powder 
of holding oxygen appears in some w T ay to depend upon 
the corpuscles, firstly, because mere serum has no greater 
power of absorbing oxygen than pure water has; and, 
secondly, because red corpuscles suspended in w 7 ater in- 
stead of serum absorb oxygen very readily. The oxygen 
thus held by the red corpuscles is readily given up by them 
for purposes of oxidation, and indeed can be removed from 
them by means of a mercurial gas-pump. It would appear 
that the connection betw T een the oxygen and the red 
corpuscles is of a peculiar nature, being a sort of loose 
chemical combination with one of their constituents, that 
constituent being the haemoglobin ; for solutions of haemo- 
globin behave towards oxygen exactly as blood does. 

The corpuscles differ chemically from the plasma, in 



PROPERTIES OF THE BLOOD. 89 

containing a large proportion of the fats and phosphates, 

all the iron, and almost all the potash, of the blood; while 
the plasma, on the other hand, contains by far the greater 
part of the chlorine and the soda. 

89. Influence of Age, Sex, and Food, upon the Blood. — 
The blood of adults contains a larger proportion of solid 
constituents than that of children, and that of men more 
than that of women ; but the difference of sex is hardly at 
all exhibited by persons of flabby, or what is called lym- 
phatic, constitution. 

Animal diet tends to increase the quantity of the red 
corpuscles; a vegetable diet and abstinence to diminish 
them. Bleeding exercises the same influence in a still more 
marked degree, the quantity of red corpuscles being dimin- 
ished thereby in a much greater proportion than that of 

other solid constituents of the blood 

90. Total Quantity of Blood in the Body. — The total 
quantity of blood contained in the body varies at different 
time>, and the precise ascertainment of its amount is very 
difficult. It may probably be estimated, on the average, 
at not than one-tenth of the weight of the body. 

91. Function of the Blood. — The function of the blood 
i- to supply nourishment to, and take away waste matters 
from, all parts of the body. It is absolutely essential to 
the life of every part of the body that it should be in such 
relation with a current of blood, that matters can pass 
freely from the blood to it, and from it to the blood, by 
transudation through the walls of the vessels in which the 
blood is contained. And this vivifying influence depends 
upon the corpuscles of the blood. The proof of these 

tements li<-- in the following experiments: If the ves- 
sels of a limb of a living animal be tied in such a manner 

to cut off the supply of blood from the limb, without 
affecting it in any other way. all the symptoms of death 
will set in. The limb will grow pale and cold, it will 

it- sensibility, and volition will no longer have power 



90 ELEMENTARY PHYSIOLOGY. 

over it ; it will stiffen, and eventually mortify and decom- 
pose. 

But, even when the death-stiffening has begun to set 
in, if the ligatures be removed, and the blood be allowed 
to flow into the limb, the stiffening speedily ceases, the 
temperature of the part rises, the sensibility of the skin 
returns, the will regains power over the muscles, and, in 
short, the part returns to its normal condition. 

If, instead of simply allowing the blood of the animal 
operated upon to flow again, such blood, deprived of its 
fibrin by whipping, but containing its corpuscles, be arti- 
ficially passed through the vessels, it will be found as 
effectual a restorative as entire blood ; while, on the other 
hand, the serum (which is equivalent to whipped blood 
without its corpuscles) has no such effect. 

It is not necessary that the blood thus artificially in- 
jected should be that of the subject of the experiment. 
Men, or dogs, bled to apparent death, may be at once and 
effectually revived by filling their veins with blood taken 
from another man, or dog ; an operation which is known 
by the name of transfusion. 

Nor is it absolutely necessary for the success of this 
operation that the blood used in transfusion should belong 
to an animal of the same species. The blood of a horse 
will permanently revive an ass, and, speaking generally, 
the blood of one animal may be replaced without injurious 
effects by that of another closely-allied species ; while that 
of a very different animal will be more or less injurious, 
and may even cause immediate death. 

92. The Lymph. — The Lymph, which fills the lymphat- 
ic vessels, is, like the blood, an alkaline fluid, consisting 
of a plasma and corpuscles, and coagulates by the separa- 
tion of fibrin from the plasma. The lymph differs from the 
blood in its corpuscles being all of the colorless kind, and 
in the very small proportion of its solid constituents, which 
amount to only about five per cent, of its weight. Lymph 



ARTERIAL AND VENOUS BLOOD. <Jl 

maw in fact, be regarded as blood tninus its red corpuscles, 
and diluted with water, so as to be somewhat less dense 
than the serum of blood, which contains about eight per 
cent, of solid matters. 

A quantity ol" fluid equal to that of the blood is prob- 
ably poured into the blood, daily, from the 1 lymphatic sys- 
tem. This fluid is in great measure the mere overflow of 
the blood itself — plasma which has exuded from the capil- 
laries into the tissues, and which has not been taken up 
again into the venous current; the rest is due to the 
absorption of chyle from the alimentary canal. 



CHAPTER IV. 

RESPIRATION. 

Section I. — Arterial and Venous Blood. 

93. High Complexity of the Blood.— The blood, the 
general nature and properties of which have been described 
in the preceding chapter, is the highly-complex product, 
not of any one organ or constituent of the body, but of all. 
Many of its features are doubtless given to it by its intrin- 
sic and proper structural elements, the corpuscles; but the 
general character of the blood is also profoundly affected 
by the circumstance, that every other part of the body 
takes, something from the blood and pours something into 
it. The blood may be compared to a river, the nature of 
the contents ofwhich is largely determined by that of the 
head-waters, and by that of the animals which swim in it ; 
but which is also very much affected by the soil over which 
it flows, by the water-weeds which cover its banks, and by 
affluents from distant regions; by irrigation-works which 

supplied from it, and by drain-pipes which flow into it. 

94. Blood rendered Venous in the Capillaries.— One of 



92 ELEMENTARY PHYSIOLOGY. 

the most remarkable and important of the changes effected 
in the blood is that which results, in most parts of the 
body, from its simply passing through capillaries, or, in 
other words, through vessels the walls of which are thin 
enough to permit a free exchange between the blood and 
the fluids which permeate the adjacent tissues (36). 

Thus, if blood be taken from the artery which supplies 
a limb, it will be found to have a bright-scarlet color ; 
while blood drawn, at the same time, from the vein of the 
limb, will be of a purplish hue, so dark that it is com- 
monly called " black blood." And, as this contrast is met 
with in the contents of the arteries and veins in general 
(except the pulmonary artery and veins), the scarlet blood 
is commonly known as arterial, and the black blood as 
venous. This conversion of arterial into venous blood takes 
place in most parts of the body, while life persists. Thus, 
if a limb be cut off and scarlet blood be forced into its 
arteries by a syringe, it will issue from the veins as blr.ck 
blood. 

95. Difference between Arterial and Venous Blood. — 
When specimens of venous and of arterial blood are sub- 
jected to chemical examination, the differences presented 
by their solid and fluid constituents are found to be very 
small and inconstant. As a rule, there is rather more 
water in arterial blood, and rather more fatty matter. But 
the gaseous contents of the two kinds of blood differ widely 
in the proportion which the carbonic-acid gas bears to the 
oxygen ; there being a smaller quantity of oxygen and a 
greater quantity of carbonic acid, in venous than in arterial 
blood. 

And it may be experimentally demonstrated, that this 
difference in their gaseous contents is the only essential 
difference between venous and arterial blood. For if ve- 
nous blood be shaken up with oxygen, or even with air, it 
gains oxygen, loses carbonic acid, and takes on the color 
and properties of arterial blood. Similarly, if arterial 



ARTERIAL AND VENOUS BLOOD. 93 

blood be treated with carbonic acid so as to be thoroughly 
saturated with thai gas, it gains carbonic acid, loses oxy- 
gen, and acquires the true properties oi* venous blood ; 
though, for a reason to be mentioned below, the change is 
not so complete in this case as in the former. The same 
result is attained, though more slowly, if the blood, in 
either case, be received into a bladder, and then placed in 
the carbonic acid, or oxygen gas; the thin moist animal 
membrane allowing the change to be effected with perfect 
se, and offering no serious impediment to the passage of 
either gas. 

96. Diffusion of Gases. — The physico-chemical processes 
involved in the exchange of carbonic acid for oxygen when 
venous is converted into arterial blood, or the reverse, in 
t\w cases mentioned above, are not thoroughly understood, 
and are probably somewhat complex. 

It is known (a) that gases', mechanically held by a fluid 
in a given proportion, tend to diffuse into any atmosphere 
to which they are exposed, until they occupy that atmos- 
phere in corresponding proportions; and (b) that gases 
separated by a dry porous partition, or simply in contact, 
diffuse into one another with a rapidity which is inversely 
proportioned to the square roots of their densities. A 
knowledge of these physical principles does, in a rough 
way, lead us to see hew the gases contained in the blood 
may effect an exchange with those in the air, whether the 
blood be freely exposed, or inclosed in a membrane. 

But the application of these principles gives no more 
than this sort of general insight. For, in the first place, 
when arterialization takes place through the walls of a 
bladder, or any other thin animal membrane, the matter is 
complicate 1 by the circumstance that moisture dissolves 
carbonic acid far more freely than it will oxygen ; hence <t 

Wei bladder has a very different action upon carbonic acW 

from that which it has upon oxygen. A moist bladder, 
partially filled with oxygen, and suspended in carbonic- 



94 ELEMENTARY PHYSIOLOGY. 

acid gas, becomes rapidly distended, in consequence of the 
carbonic-acid gas passing into it with much greater rapid- 
ity than the oxygen passes out. Secondly, the gases of 
the blood are not held in a merely mechanical way in it ; 
the oxygen seems to be loosely combined with the red 
corpuscles (88), and there is reason to think that a great 
part, at least, of the carbonic acid, is chemically connected, 
in a similarly loose way, with certain saline constituents 
of the serum. Hence the arteriaiization of blood in the 
lungs seems to be a very mixed process, partly physical, 
and yet, to a certain extent, chemical, and consequently 
very difficult to analyze. 

The same may also be said of the change from arterial 
to venous blood in the tissues. Owing to the peculiar 
relation of oxygen to the red blood-corpuscles, the process 
which takes place in the tissues is not a simple inter- 
change by diffusion of the oxygen of the blood for the 
carbonic acid of the tissues ; on the contrary, the oxygen 
is given up for purposes of oxidation, the demand being 
determined by the supply of oxidizable materials in the 
tissue, while the blood, poor in carbonic acid, takes up, 
apparently by an independent action, a quantity of that 
gas from the tissues rich in it. 

Hence venous blood is characterized not only by the 
large amount of carbonic acid present, but also by the fact 
that the red corpuscles have given up a good deal of their 
oxygen for the purposes of oxidation, or, as the chemists 
would say, have become reduced. This is the reason why 
arterial blood is not so easily converted into venous blood 
by exposure to carbonic acid as venous blood into arterial 
by exposure to oxygen. There is, in the former case, a 
want of some oxidizable substance to carry off the oxygen 
from and so to reduce the red corpuscles. When such an 
oxidizable substance is added (as, for instance, a salt of 
iron), the blood at once and immediately becomes com- 
pletely venous. 



ARTERIAL AND VENOUS BLOOD. 95 

Practically we may say that the most important differ- 
ence between venous and arterial blood is not bo much the 
relative quantities of carbonic acid as that the red corpus- 
cles of venous blood have lost a good deal of oxygen, are 

reduced, and ready at once to take up any oxygen offered 
to them. 

97. Cause of the Change of Color in Blood. — The pause 
of the change of color of the blood — of its darkening when 
exposed to carbonic acid, and its brightening when under 
the influence of oxygen — is not thoroughly understood. 

re is reason to think, however, that the red corpuscles 
are rendered somewhat flatter by oxygen gas, while they 
distended by the action of carbonic acid (76). Under 
the former circumstances they may, not improbably, reflect 
the light more strongly, so as to give a more distinct colora- 
tion t<> tin 4 blood ; while, under tin 1 latter, they may reflect 

» light, and. in that way, allow the blood to appear 
darker and duller. 

This, however, is not the whole of the matter; for solu- 
tions of haemoglobin or of blood-crystals (81), even when 
perfectly free from actual blood-corpuscles, change in color 
from scarlet to purple, according as they gain or lose oxy- 
gen. It has already been stated (88) that oxygen most 
probably exists in the blood in loose combination with 
haemoglobin. But, further, there is evidence to show that 

- .hit ion of haemoglobin, when thus loosely combined 
with oxygen, has a scarlet color, while a solution of 
hemoglobin, deprived of oxygen, has a purplish hue. 
Hence arterial blood, in which the haemoglobin is richly 
provided with oxygen, would naturally be scarlet, while 
Venous blood, which not only contains an excess of car- 
bonic acid, but whose haemoglobin also has lost a great 

deal of its oxygen, would be purple. 

98. Conditions of its Chemical Changes. — Whatever may 
1m- their explanation, however, the facts arc certain (1), 

that arterial blood, separated by only a thin membrane 



96 ELEMENTARY PHYSIOLOGY. 

from carbonic acid, or from a fluid containing a greater 
amount of carbonic acid than itself, and also carrying cer- 
tain oxidizable materials, becomes venous ; and (2) that 
venous blood, separated by only a thin membrane from 
oxygen, or a fluid containing a greater proportion of free 
oxygen than itself, becomes arterial. 

In these facts lies the explanation of the conversion of 
scarlet blood into dark blood as it passes through the capil- 
laries of the body, for the latter are bathed by the juices 
of the tissues, which contain carbonic acid, the product of 
their waste and combustion, in excess, together with highly- 
oxidizable matters. On the other hand, if we seek for the 
explanation of the conversion of the dark blood in the veins 
into the scarlet blood of the arteries, we find, first, that the 
blood remains dark in the right auricle, the right ventricle, 
and the pulmonary artery ; second, that it is scarlet not 
only in the aorta, but in the left ventricle, the left auricle, 
and the pulmonary veins. 

Obviously, then, the change from venous to arterial 
takes place in the pulmonary capillaries, for these are the 
sole channels of communication between the pulmonary 
arteries and the pulmonary veins. 

Section II. — The Lungs and their Office. 

99. The Essence-nature of Respiration. — But what are 
the physical conditions to which the blood is exposed in 
the pulmonary capillaries ? 

These vessels are very wide, thin-walled, and closely 
set, so as to form a net-work with very small meshes, 
which is contained in the substance of an extremely thin 
membrane. This membrane is in contact with the air, so 
that the blood in each capillary of the lung is separated 
from the air by only a delicate pellicle formed by its own 
wall and the lung-membrane. Hence an exchange very 
readily takes place b?tween the blood and the air ; the 



THE LUNGS AND THEIR OFFICE. 07 

latter gaining moisture and oarbonic acid, and losing oxy- 
gen - 

This is the essential step in respiration: thai it really 
takes place may be demonstrated very readily, by the 
experiment described in the firsl Chapter, in which air 
expired was proved to differ from air inspired, by e< n- 

taining more heat, more water, more carbonic acid, and 

less _ i ; or, on the other hand, by putting a liga- 
ture on the windpipe of a living animal so as to prevent 
air from passing into or out of the lungs, and then exam- 
ining the contents of the heart atid great vessels. The 
blood on both >id<*s of the heart, and in the pulmonary 
veins and aorta, will be found to be as completely venous 
as in the ven« cava* and pulmonary artery. 

But, though the passage of carbonic-acid gas and hot 
watery vapor out of the blood and of oxygen into it is the 
lencc of the respiratory procesi — and thus a membrane 
with bh.od <>n one side, and air on the other, is all that is 
absolutely necessary to effect the purification of the bl< od 
— yet the accumulation of carbonic acid is bo rapid, and 
the need for oxygen BO incessant, in all parts of the human 
body, that the former could not be cleared away, nor the 
latter supplied, with adequate rapidity, without tin* aid 
of extensive and complicated accessory machinery — the 
arrangement and working of which must next be carefully 

studied. 

100. Mechanism of Respiration. — The back of the month 
or pharynx communicates by two channels with the exter- 
nal air [see Fig. 49). One of these is formed by the nasal 
ges, which cannot be closed by any muscular appa 
ratns of their own: the other is presented by the mouth, 

which can be sbul or opened at will. 

' Th«- «tij<i<-r:t mutt guard trimaetf tgUMl th<- Idea that uteris] M<>«"! 

enrU.rtK- add, Hid renooi t>lo<*l I through the lie - 

\>\<«x\ ]<>><■* only nir Mid ! : i r t * 1 uteri*] t>l<x*l. in DOM iirj Tf r «h:l' 

tlnnca, loses only a part of In Mood, however Tenons, there It in b< 

b tli*' brightest uteris] blood, thin i- sctasHy more 
••;ii' add ttuu 
7 



98 



ELEMENTARY PHYSIOLOGY. 



Immediately behind the tongue, at the lower and front 
part of the pharynx, is an aperture — the glottis (Fig. 22, 
Gl.) — capable of being closed by a sort of lid — the epiglot- 
tis — or by the shutting together of its side boundarieSj 
formed by the so-called vocal chords. The glottis opens 
into a chamber with cartilaginous walls — the larynx ; and, 
leading from the larynx downwards along the front part 
of the throat, where it may be very readily felt, is the 
trachea^ or windpipe (Fig. 22, Tr.). 




Back View of the Neck and- Thorax of a Hitman" Subject from which the 
Vertebral Column anti> whole Posterior Wall of the Che3t are supposed 
to be removed. 

J/., mouth; Gl., glottis; Tr., trachea: L.L., left lung-; R.L., right lung; Br., 
bronchus; P. A., pulmonary artery ; P.Y., pulmonary veins; Ao., aorta; Z>., dia- 
phragm ; H., heart; V.C.I., vena cava inferior. 

If the trachea be handled through the skin, it will be 
found to be firm and resisting. Its walls are, in fact, 
strengthened by a series of cartilaginous hoops, which 
hoops are incomplete behind, their ends being united only 
by muscle and membrane, where the trachea comes into 
contact with the gullet, or oesophagus. The trachea passes 



THE LUNGS AND THEIR OFFICE. 



99 



into the thorax, and there divides into two branches, a 
right and a left, which are termed the bronchi (Fig. 22, 
/>/•.). Each bronchus enters the lung of its own Bide, and 
then breaks up into a great number of smaller branches, 
which are called the br<>u<'/tidl tulxs. As these diminish in 
. the cartilages, which are continued all through the bron- 
chi and their large ramifications, become smaller and event- 
ually disappear, so that the walls oi the smallest bronchial 
tubes arc entirely muscular or membranous. Thus, while 








Fig. 24. 







Fig. 26. 



:th the ultim.it.- bronchia] tube (a) which <>j»cns into 

(ZTlifled twentv <<: 

•ii.iti • vi.w of an sir-cell (Fig. 28) Been \n section: ". epithelium; 
b\ r»artn t cells, in tii.- thickness of which tin- espinaiiefl run. 

• rtion of injected lun- magnified: //. the espillariei spr ead orer the 
'•vail- of nche* of arteries and reins. 

-'•'•. — Portlcm highly magnified. 



100 ELEMENTARY PHYSIOLOGY. 

the trachea and bronchi are kept permanently open and 
pervious to air by their cartilages, the smaller bronchial 
tubes may be almost closed by the contraction of their 
muscular walls. 

The -finer bronchial tubes end at length in elongated 
dilatations, about ^V^h of an inch in diameter on the aver- 
age (Fig. 23). Each of these dilatations is beset with, or 
perhaps rather is made up of, little sacs, which open irreg- 
ularly into the cavity of the dilatation. These sacs are 
the air-cells. The very thin walls (Fig. 24) w T hich separate 
these air-cells are supported by much delicate and highly- 
elastic tissue, and carry the wide and close-set capillaries 
into which the ultimate ramifications of the pulmonary 
artery pour its blood (Fig. 26). Thus, the blood contained 
in these capillaries is exposed on both sides to the air — 
being separated from the air-cell on either hand only by 
the very delicate pellicle which forms the wall of the capil- 
lary, and the lining of the air-sac. 

101. The Provision for the Renewal of Air. — Hence no 
conditions can be more favorable to a ready exchange be- 
tween the gaseous contents of the blood and those of the 
air in the air-cells, than the arrangements which obtain in 
the pulmonary capillaries ; and, thus far, the structure of 
the lung fully enables us to understand how it is that the 
large quantity of blood poured through the pulmonary cir- 
culation becomes exposed in very thin streams, over a large 
surface, to the air. But the only result of this arrangement 
would be, that the pulmonary air would very speedily lose 
all its oxygen, and become completely saturated with car- 
bonic acid, if special provision were not made for its being 
incessantly renewed. 

102. Inspiration and Expiration. — If an adult man, 
breathing calmly in the sitting position, be watched, the 
respiratory act will be observed to be repeated thirteen to 
fifteen times every minute. Each act consists of certain 
components which succeed one another in a regular rhyth- 



THE LUNGS AND THEIR OFFICE. 101 

mica] order. First, tin 4 breath is drawn in, or inspired; 
immediately afterwards it is driven out, or expired/ and 
those successive acts of inspiration and expiration are 

followed by a brief pause. Thus, just as in the rhythm o( 
the heart the auricular systole, the ventricular systole, and 
then a pause, follow in regular order ; so in the chest, the 
inspiration, the expiration, and then a pause, succeed cue 
another. At each inspiration of an adult well-irrown man, 
about thirty cubic inches o( air are inspired; and at each 

piration the same, or a slightly smaller, volume (allow- 
ing for the increase of temperature of the air so expired) 
i- given out of the body. 

103. Differences between Inspired and Expired Air. — 

The expirel air differs from the air inspired in the fol- 
lowing particular- : 

Whatever the temperature of the external air is, 
that expire. 1 is nearly as hot as the blood, or lias a tem- 
perature between 90 and 100°. 

(/>) However dry the external air may be, that expired 
i- quite or nearly saturated with watery vapor. 

| Though ordinary air contains nearly ^,100 parts of 

jrgen, and 7,900 of nitrogen, with not more than three 
part- of carbonic acid, in 10,000 parts, expired air contains 
about 41<> parts <»f carbonic acid, and only between 1,500 
and 1,600 parts <>f oxygen ; while the quantity of nitrogen 
suffers little or no change. Speaking roughly, air which 
has been breathed once has gained live per cent, of car- 
bonic acid, and lo-t five percent, ofoxygen. 

The expire! air contains, in addition, a greater or less 
quantity of animal matter of a highly-decomposable char- 

er, 

('/» Verj close analysis of the expired air show-, firstly, 
that the quantity of oxygen which disappears is always 
_litlyin i of the quantity of carbolic acid sup- 

plied; and. secondly, that the nitrogen i^ variable — the 
expired nitrogen \* _ imetimea Blightly in excess of, 



102 ELEMENTARY PHYSIOLOGY. 

sometimes slightly less than that inspired, and sometimes 
remaining stationary. 

104. The Amount of Work don* by the Lungs. — From 
three hundred and fifty to four hundred cubic feet of air 
are thus passed through the lungs of an adult man taking 
little or no exercise, in the course of twenty-four hours ; 
and are charged with carbonic acid, and deprived of oxy- 
gen, to the extent of nearly five per cent. This amounts 
to about eighteen cubic feet of the one gas taken in, and 
of the other given out. Thus, if a man be shut up in a 
close room, having the form of a cube seven feet in the 
side, every particle of air in that room will have passed 
through his lungs in twenty-four hours, and a fourth of the 
oxygen it contained will be replaced by carbonic acid. 

The quantity of carbon eliminated in the twenty-four 
hours is pretty clearly represented by a piece of pure char- 
coal weighing eight ounces. 

The quantity of water given off from the lungs in the 
twenty-four hours varies very much, but may be taken on 
the average as rather less than half a pint, or about nine 
ounces. It may fall below this amount, or increase to 
double or treble the quantity. 

Section III. — The Respiratory Mechanism. 

105. Mechanism of the Respiratory Movements. — The 

mechanical arrangements by w^hich the respiratory move- 
ments, essential to the removal of the great mass of effete 
matters, and the importation of the large quantity of oxy- 
gen indicated, are effected, may be found in — (a) the elas- 
ticity of the lungs ; (b) the mobility of the sides and bottom 
of the thoracic cavity in which the lungs are contained. 

The thorax may be regarded as a completely shut coni- 
cal box, with the small end turned upwards, the back of 
the box being formed by the spinal column, the sides by 
the ribs, the front by the breastbone, the bottom by the 
diaphragm, and the top by the root of the neck (Fig. 22). 



THE RESPIRATORY MECHANISM. 10;} 

The two lungs occupy almost all the cavity of this box 
which is not taken up by the heart. Each is inclosed in 
its serous membrane, the pleura, a double bag (very simi- 
lar to the pericardium, the duet* difference being that the 
outer bag of each pleura is, over the greater part of its ex- 
tent, quite firmly adherent to the walls of the chest and 
the diaphragm (see Fig. 1*2), while the outer bag of the 
pericardium is for the most part loose), the inner bag 
closely covering the lung and the outer forming a lining 
t«» the cavity of the chest. So long as the walls of the 
thorax are entire, the cavity of each pleura is practically 
obliterated, that layer of the pleura which covers the lung 
beitig in close contact with that which lines the wall of the 
chest ; but if a small opening be made into the pleura, the 
lung at once shrinks to a comparatively small size, and 
thus develops a great cavity between the two layers of the 
pleura. If a pipe be now fitted into the bronchus, and air 
blown through it, the lung is very readily distended to its 
full siz"; but, on being left to itself, it collapses, the air 
being driven out again with some force. The abundant 
elastic tissues of the walls of the air-cells are, in fact, so 
di -posed as to be greatly stretched when the lungs are 
full ; and, when the cause of the distention is removed, 
this elasticity comes into play and drives the greater part 
of the air out again. 

The lungs are kept distended in the dead subject, so 
lon L r as tin* walls of the chest are entire, by the pressure 
of fche atmosphere. For though the elastic tissue is all the 
while pulling, as it were, at the layer of pleura which covers 
the lung, and attempting to separate it from that which 
lines the chest, it cannot produce such a separation with- 
out developing a vacuum between these two layers. To 
effect this, the elastic tiscue mus1 pull with a force greater 

than that of the external air (or fifteen pounds to the 
Square inch), an effort far beyond its powers, which do not 

rqual more than one-fourth of a pound on the square inch. 



104 ELEMENTARY PHYSIOLOGY. 

But the moment a hole is made in the pleura, the air enters 
into its cavity, the atmospheric pressure inside the lung is 
equalized by that outside it, and the elastic tissue, freed 
from its opponent, exerts its full power on the lung. 

106. Walls of the Bronchial Tubes-Cilia. — The lungs 
are elastic, whether alive or dead. During life the air 
which they contain may be further affected by the contrac- 
tility of the muscular walls of the bronchial tubes. If 
water is poured into the lungs of a recently-killed animal, 
and a series of electric shocks is then sent through the 
bronchial tubes, the latter contract, and the water is forced 
out. Lastly, during life a further source of motion in the 
bronchial tubes is provided by the cilia — minute filaments 
attached to the epithelium of the tubes, which incessantly 
vibrate backwards and forwards, and work in such a man- 
ner as to sweep liquid and solid matters outwards, or tow- 
ards the trachea. 

107. Movements of the Chest-Walls. — The ribs are at- 
tached to the spine, so as to be freely movable upon it ; 
but, when left to themselves, they take a position which is 
inclined obliquely downwards and forwards. 1 Two sets of 
muscles, called intercostals, pass between the successive 
pairs of ribs on each side. The outer set, called external 
intercostals (Fig. 27, A), run from the rib above, obliquely 
downwards and forwards, to the rib below. The other set, 
internal intercostals (Fig. 27, .2?), cross these in direction, 
passing from the rib above, downwards and backwards, to 
the rib below. 

The action of these muscles is somewhat puzzling at 
first, but is readily understood if the fact, that when a 
muscle contracts it tends to make the distance between its 
two ends as short as possible, be borne in mind. Let a and 
bj in Fig. 28, A, be two parallel bars, movable by their 

1 I purposely neglect the consideration of the cartilages of the ribs, and some other 
points, in order not to complicate the question unnecessarily. It may, however, be 
stated that those fibres of the internal intercostals which are situate between the car- 
tilages act like the external, and raise the ribs. 



THE RESPIRATORY MECHANISM. 



105 



ends upon the upright <\ which may be regarded as at the 

back of the apparatus, then a line directed from x to y will 
be inclined downwards and forwards, and one from 10 to 2 
will be directed downwards and backwards. Now, it is 
obvious that there is one position of the rods, and one only, 
in which the points X and y are at the shortest possible dis- 
tance, and one position only in which the points ir and z 
are at the shortest possible distance; and these are, for 




VlBW Of POUI Hrr.s OF tiif. DoG with t;ik [NTEBOOSTAL IfUBOISS. 

a. the l*»nv ril»: ft, the cartilage; c, the junction of bone and cartilage; ./. on- 
L e^oaamed, portions of the sternum, a. external Intercostal mnacle; /»'. in- 
ternal intercostal mnacle. In the middle Interspace, the external Intercostal has been 
removed t.. show the Internal LntercoBtal beneath it. 



X and y the position B, and forte and z the position C. 
These positions are respectively such thai the point- sb, y, 
and to, z, are at the ends of Btraighf lines perpendicular t<> 
both rods. 

Thus, to bring a; and y into this position, the parallel 



106 



ELEMENTARY PHYSIOLOGY. 



rods in A must move upwards ; and, to bring w and z into 
it, they must move in the opposite way. 

If the simple apparatus just described be made of wood, 
hooks being placed at the points x, y, and w, z ; and an 
elastic band, as long when left to itself as the shortest dis- 
tance between these points, be provided with eyes which 
can be readily put on to or taken off these hooks : it will 
be found that when the bars are in the horizontal position, 
A, the elasticity of the band, when hooked on to x and y, 



a w jt 





A 



Fig. 28. 

Diagkam op Models illustrating the Action of the External and Internal 
Intercostal Muscles. 

B, inspiratory elevation ; C. expiratory depression. 



will bring them up into the position shown in Fig. 28, B; 
while, if hooked on to w and 2, it will force them down 
into the position shown in Fig. 28, C. 

Substitute the contractility of the external and internal 
intercostal muscles for the elasticity of the band, and the 
latter will precisely exemplify their action ; and it is thus 
proved that the external intercostals must raise, and the 
internal intercostals must depress, the bony ribs. 

108. The Diaphragm. —The diaphragm is a great par- 
tition situated between the thorax and the abdomen, and 
always concave to the latter and convex to the former (FiV. 



THE RESPIRATORY MECHANISM. 



101 



1, D). From its middle, which is tendinous, muscular 
fibres extend downwards and outwards to the ribs, and 
two, especially strong masses, which are called the pillars 
of the diaphragm^ to the spinal column (Fig. 29). When 
these muscular fibres contract, therefore, they tend to make 
the diaphragm flatter, and to increase the capacity of the 
thorax at the expense of that of the abdomen, by pulling 
down the bottom of the thoracic box (Fig. 30). 




Fie. 29. 

TlIK P.'APIIRAGM OF A D<><; VIEWED FROM THE LoWF.R OR ABDOMINAL SlDF. 

V <' I., the rent eaya Inferior; o.. the (esophagus; A<>.. th«- aorta; the brotd white 
illy distinguished from the radiating muscular fibres (<4) 

which pass down to the rfta and into the pillars | ( ' />> in l'ront of tin- virtehr.f. 

109. A?tion of Different Parts compared. — Let us now 

-• msi ler what would be the result of the action of the parts 

*ii<' respiratory apparatus, which have beep described, 
if the diaphragm alone should begin t<> contract at regular 
intervals. 



108 ELEMENTARY PHYSIOLOGY. 

When it contracts it increases the vertical dimensions 
of the thoracic cavity, and tends to pull away the lining of 
the bottom of the thoracic box from that which covers the 
bases of the lungs ; but the air immediately rushing in at 
the trachea, proportionately increases the distention of the 
lungs, and prevents the formation of any vacuum between 
the two pleurae of either lung in this region. When the 
diaphragm ceases to contract, so much of the elasticity of 
the lungs as was neutralized by the contraction of the dia- 
phragm, comes into play, and the extra air taken in is 
driven out again. We have, in short, an inspiration and 
an expiration. 

Suppose, on the other hand, that, the diaphragm being 
quiescent, the external intercostal muscles contract. The 
ribs will be raised from their oblique position, the antero- 
posterior dimensions of the thoracic cavity will be in- 
creased, and the lungs will be distended as before to bal- 
ance the enlargement. If, now, the external intercostals 
relax, the action of gravity upon the ribs, the elasticity of 
the cartilages, and, more especially, that of the lungs, will 
alone suffice to bring back the ribs to their previous posi- 
tions, and to drive out the extra air ; but this expiratory 
action may be greatly aided by the contraction of the in- 
ternal intercostals. 

Section IV. — Inspiration and Expiration. 

110. Accessory Muscles. — Thus it appears that we may 
have either diaphragmatic respiration, or costal respira- 
tion. As a general rule, however, not only do the two 
forms of respiration coincide and aid one another — the con- 
traction of the diaphragm taking place at the same time 
with that of the external intercostals, and its relaxation 
with the contraction of the internal intercostals — but sun- 
dry other accessory agencies come into play. Thus, the 
muscles which connect the ribs with parts of the spine 
above them, and with the shoulder, may, more or less ex- 



INSPIRATION AND EXPIRATION. 109 

tensively, assist inspiration; while those which connect 
the ribs and breastbone with the pelvis, and form the front 
and side walls o( the abdomen, are powerful aids to expi- 
ration. In fact, they assist expiration iii two ways: first, 
directly, by pulling down the ribs; and next, indirectly, 
by pressing the viscera o( the abdomen upwards against 
the under surface {){' the diaphragm, and bo driving the 
Boor o( the thorax upwards. 

It is for this reason that, whenever a violent expiratory 
effort is made, the walls of tin 1 abdomen are obviously flat- 
tened and driven towards the spine, the body being at the 
same time bent forwards. 

In taking a deep inspiration, on the other hand, the 

lis of the abdomen are relaxed and become convex, the 

viscera being driven against them by the descent of the 

diaphragm — the spine is straightened, the head thrown 

back, and the shoulders outwards, so as to afford the great- 
mechanical advantage to all the muscles which can 
elevate the ribs. 

111. How Respiration differs in the Sexes. — It is a re- 
markable circumstance that the mechanism of respiration 
is somewhat different in the two sexes. In men, the dia- 
phragm takes the larger share in the process, the upper 
ribs moving comparatively little ; in women, the reverse is 
.tin respiratory act being more largely the result 
of the movement of the ribs. 

Sighing is a deep and prolonged inspiration. "Sniff- 
ing™ 18 a more rapid inspiratory act, in which the month 
ifl kept shut, and the ail- made to pass through the nose. 

Coughing \> a violent expiratory act. A deep inspira- 
tion being first taken, the glottis is closed and then IhiisI 
(.p<-n by the violent compression of the air contained in the 

lungs by th<- contraction of the expiratory muscles, the 
diaphragm being relaxed and the air driven through the 
mouth. In sneezing, on the contrary, the cavity of the 

month being -hut off from the pharynx by the approxima- 



110 



ELEMENTARY PHYSIOLOGY. 



tion of the soft palate and the base of the tongue, the air 
is forced through the nasal passages. 

112. Residual, Supplemental, and Tidal Air. — It thus 
appears that the thorax, the lungs, and the trachea, consti- 
tute a sort of bellows without a valve, in which the thorax 
and the lungs represent the body of the bellows, while the 





Fig. 30. Fig. 81. 

Diagrammatic Sections of the Body in 

Fig. 30, inspiration ; Fig-. 31, expiration. 7>\, trachea; St, sternum; /)., diaphragm; 
Ab., abdominal walls. The shading roughly indicates the stationary air. 



trachea is the pipe ; and the effect of the respiratory move- 
ments is just the same as that of the approximation and 
separation of the handles of the bellows, which drive out 
and draw in the air through the pipe. There is, however, 
one difference between the bellows and the respiratory ap- 
paratus, of great importance in the theory of respiration, 



INSPIRATION AND EXPIRATION. HI 

though frequently overlooked ; and that is, that the sides 
of the bellows can be brought close together so as to force 
out all, or nearly all, the air which they contain ; while the 
walls of the chest, when approximated as much as possible, 
still inclose a very considerable cavity (Fig. 31) ; so that, 
even after the most violent expiratory effort, a very large 
quantity of air is left in the lungs. 

The amount of this air which cannot be got rid of, and 
is called Residual air, is, on the average, from seventy-five 
to one hundred cubic inches. 

About as much more in addition to this remains in the 
chest after an ordinary expiration, and is called Supple- 
m< rUal air. 

In ordinary breathing, twenty to thirty cubic inches 
of what is conveniently called Tidal air pass in and out. 
It follows that, after an ordinary inspiration, 100 + 100 + 
30 = 230 cubic inches may be contained in the lungs. 
By taking the deepest possible inspiration, another one 
hundred cubic inches, called Complemental air, may be 
added. 

113. Office of the Stationary Air. — It results from these 
data that the lungs, after an ordinary inspiration, contain 
about two hundred and thirty cubic inches of air, and that 
only about one-seventh to one-eighth of this amount is 
breathed out and taken in again at the next inspiration. 
Apart from the circumstance, then, that the fresh air in- 
spired has to fill the cavities of the hinder part of the 
mouth, and the trachea, and the bronchi, if the lungs were 
mere bags fixed to the ends of the bronchi, the inspired air 
would descend as far only as to occupy that one-fourteenth 
to one-sixteenth part of each bag which was nearest to the 
bronchi, whence it would be driven out again at the next 
expiration. But, as the bronchi branch out into a pro- 
digious number of bronchial tubes, the inspired air can 
only penetrate for a certain distance along these, and can 
never reach the air-cclK at all. 



112 ELEMENTARY PHYSIOLOGY. 

Thus the residual and supplemental air taken together 
are, under ordinary circumstances, stationary — that is to 
say, the air comprehended under these names merely shifts 
its outer limit in the bronchial tubes, as the chest dilates 
and contracts, without leaving the lungs; the tidal air, 
alone, being that which leaves the lungs and is renewed 
in ordinary respiration. 

It is obvious, therefore, that the business of respiration 
is essentially transacted by the stationary air, which plays 
the part of a middleman between the two parties — the 
blood and the fresh tidal air — who desire to exchange 
their commodities, carbonic acid for oxygen, and oxygen 
for carbonic acid. 

Now, there is nothing interposed between the fresh 
tidal air and the stationary air ; they are aeriform fluids, 
in complete contact and continuity, and hence the ex- 
change between them must take place according to the 
ordinary laws of gaseous diffusion. 

114. Composition of the Stationary Air. — Thus, the 
stationary air in the air-cells gives up oxygen to the blood, 
and takes carbonic acid from it, though the exact mode in 
which the change is effected is not thoroughly understood. 
By this process it becomes loaded with carbonic acid, and 
deficient in oxygem though to what precise extent is not 
known. But there must be a very much greater excess of 
the one, and deficiency of the other, than is exhibited by 
inspired air, seeing that the latter acquires its composition 
by diffusion in the short space of time (four to five seconds) 
during which it is in contact with the stationary air. 

In accordance with these facts, it is found that the air 
expired during the first half of an expiration contains less 
carbonic acid than that expired during the second half. 
Further, when the frequency of respiration is increased 
without altering the volume of each inspiration, though 
the percentage of carbonic acid in each inspiration is 
diminished, it is not diminished in the same ratio as that 



INSPIRATION AND EXPIRATION. 113 

in which the number o( inspirations increases ; and hence 
more carbonic acid is got rid of in a given time. 

Thus, if the number of inspirations per minute is in- 
creased from fifteen to thirty, the percentage of carbonic 
acid evolved in the second case remains more than half of 
what it was in the first case, and hence the total evolution 
i- greater. 

115. The Nervous System controls Respiration.— Of the 
various mechanical aids to the respiratory process, the nature 
and workings of which have now been described, one, the 
elasticity of the lungs, is of the nature of a dead, constant 
force. The action of the rest of the apparatus is under 
the control of the nervous system, and varies from time to 
time. 

As the nasal passages cannot be closed by their own 
action, air lias always free access to the pharynx; but the 
glottis, or entrance to the windpipe, is completely under 
the control of the nervous system — the smallest irritation 
about tht 4 mucous membrane in its neighborhood being 
conveyed, by its nerves, to that part of the cerebro-spinal 
axis which is called the medulla oblongata (see 328). The 
medulla oblongata, thus stimulated, gives rise, by a process 
which will be explained hereafter, termed reflex action, to 
the contraction of the muscles which close the glottis, and 
commonly, at the same time, to a violent contraction of the 
expiratory muscles, producing a cough (see 111). 

The muscular fibres of the smaller bronchial tubes, no 
is than the respiratory pump itself, formed by the walls 
and floor of the thorax, are under the complete control of 
the nerves which supply the muscles, and wdiich are brought 
into action in consequence of impressions conveyed to that 
pari of the brain which is called the medulla oblongata, by 
the pneumogastric and other nerves. 

116. Respiration and Circulation compared. — From 
what has been said, it is obvious thai there are many 
analogies between the circulatory and the respiratory ap- 

8 



114 ELEMENTARY PHYSIOLOGY. 

paratus. Each consists, essentially, of a kind of pump 
which distributes a fluid (aeriform in the one case, liquid 
in the other) through a series of ramified distributing-tubes 
to a system of cavities (capillaries or air-cells), the volume 
of the contents of which is greater than that of the tubes. 

In each, the pump is the cause of the motion of the 
fluid, though that motion may be regulated, locally, by the 
contraction, or relaxation, of the muscular fibres contained 
in the walls of the distributing-tubes. But, while the 
rhythmic movement of the heart chiefly depends upon a 
nervous apparatus placed within itself, that of the respira- 
tory apparatus results mainly from the operation of a ner- 
vous centre lodged in the medulla oblongata. 

Section V. — Effects of Respiration. 

117. Secondary Phenomena.— As there are certain sec- 
ondary phenomena which accompany, and are explained 
by, the action of the heart, so there are secondary phe- 
nomena which are similarly related to the working of the 
respiratory apparatus. These are — (a) the respiratory 
sounds, and (b) the effect of the inspiratory and expiratory 
movements upon the circulation. 

118. The Respiratory Murmurs. — The respiratory sounds 
or murmurs are audible when the ear is applied to any part 
of the chest which covers one or other of the lungs. They 
accompany inspiration and expiration, and very much re- 
semble the sounds produced by breathing through the 
mouth, when the lips are so applied together as to leave a 
small interval. Over the bronchi the sounds are louder 
than over the general surface. It would appear that these 
sounds are produced by the motion of the air along the 
air-passages. 

119. Inspiration assists the Circulation. — In consequence 
of the elasticity of the lungs, a certain force must be ex- 
pended in distending them, and this force is found experi- 
mentally to become greater and greater the more the lung 



EFFECTS OF RESPIRATION. 115 

is distended ; just as, in stretching a piece of India-rubber, 
more force is required to stretch it a good deal than is 
needed to stretch it only a little. Hence, when inspiration 
takes place, and the lungs aiv distended with air, the heart 
and the great vessels in the chest are subjected to a less 
pressure than are the blood-vessels of the rest of the bod}^ 

For the pressure of the air contained in the lungs is 
exactly the same as that exerted by the atmosphere upon 
the surface of the body; that is to say, fifteen pounds on 
the square inch. Hut a certain amount of this pressure 

rted by the air in the lungs is counterbalanced by the 
elasticity of the distended lungs. Say that in a given con- 
dition of inspiration a pound pressure on the square inch is 
needed to overcome this elasticity, then there will be only 
fourteen pounds pressure on every square inch of the heart 
and great vessels. And hence the pressure on the blood 
in these vessels will be one pound per square inch less 
than that on the veins and arteries of the rest of the body. 
If then- were no aortic, or pulmonary, valves, and if the 
composition of the vessels, and the pressure upon the blood 
in them, were everywhere the same, the result of this ex- 

- of pressure on the surface would be, to drive all the 
blood from the arteries and veins of the rest of the body 
into the heart and great vessels contained in the thorax. 
And thus the diminution of the pressure upon the thoracic 
blood-cavities produced by inspiration would, practically, 
suck the blood from all parts of the body towards the 
thorax. Hut the suction thus exerted, while it hastened 
the flow of blood to the heart in the veins, would equally 
oppose the flow from the heart to the arteries, and the 
two effects would balance one another. 

120. Unequal Pressures facilitate the Circulation. — As 

a matter of fact, however, we know — 

(1.) Thai the blood in the greal arteries is constantly 
under a very considerable pressure, exerted by their elas- 
tic walls ; while thai of the veins is under little pressure. 



116 ELEMENTARY PHYSIOLOGY. 

(2.) That the walls of the arteries are strong and resist- 
ing, while those of the veins are weak and flabby. 

(3.) That the veins have valves opening towards the 
heart ; and that, during the diastole, there is no resistance 
of any moment to the free passage of blood into the heart ; 
while, on the other hand, the cavity of the arteries is shut 
off from that of the ventricle during the diastole, by the 
closure of the semilunar valves. 

Hence it follows that equal pressures applied to the 
surface of the veins and to that of the arteries must pro- 
duce very different effects. In the veins the pressure is 
something which did not exist before ; and, partly from 
the presence of valves, partly from the absence of resist- 
ance in the heart, partly from the presence of resistance in 
the capillaries, it all tends to accelerate the flow of blood 
towards the heart. In the arteries, on the other hand, the 
pressure is only a fractional addition to that which existed 
before ; so that, during the systole, it only makes a com- 
paratively small addition to the resistance which has to be 
overcome by the ventricle ; and, during the diastole, it 
superadds itself to the elasticity of the arterial walls in 
driving the blood onwards towards the capillaries, inas- 
much as all progress in the opposite direction is stopped 
by the semilunar valves. 

It is, therefore, clear that the inspiratory movement, on 
the whole, helps the heart, inasmuch as its general result 
is to drive the blood the way that the heart propels it. 

121. Effect of Expiration on the Circulation. — In ex- 
piration, the difference between the pressure of the atmos- 
phere on the surface, and that which it exerts on the con- 
tents of the thorax through the lungs, becomes less and 
less in proportion to the completeness of the expiration. 
Whenever, by the ascent of the diaphragm and the descent 
of the ribs, the cavity of the thorax is so far diminished 
that pressure is exerted on the great vessels, the veins, 
owing to the thinness of their walls, are especially affected, 



EFFECTS OF RESPIRATION. 117 

and a check is given to the flow of blood in them, which 
inav become visible as a venous pulse in the greal vessels 
of the neck. In its effect on the arterial trunks, expira- 
tion, like inspiration, is, on the whole 4 , favorable to the 
circulation ; the increased resistance to the opening of the 
valves during the ventricular Bystole being more than 
balanced by the advantage gained in the addition of the 
expiratory pressure to the elastic reaction of the arterial 
walls during the diastole, 

When the skull of a living animal is laid open and the 
brain exposed, the cerebral substance is seen to rise and 
fall synchronously with the respiratory movements; the 
rise corresponding with expiration, and being caused by 
the obstruction thereby offered to the flow of the blood in 
the veins of the head and neck. 

122. Stoppage of the Heart by Distention of the Lungs. 
— Hitherto, 1 have supposed the air-passages to be freely 
open during the inspiratory and expiratory movements. 
But, if, the lungs being distended, the mouth and nose are 
closed, and a strong expiratory effort is then made, the 
heart's action may be stopped altogether. 1 And the same 
result occurs if, the lungs being partially emptied, and the 
nose and mouth closed, a strong inspiratory effort is made. 
In the latter case the excessive distention of the right side 
of the heart, in consequence of the flow of blood into it, 
may be the cause of the arrest of the heart's action ; but, in 
the former, the reason of the stoppage is not very clear, 

123. Circumstances modifying Respiration. — The activ- 
ity of the respiratory process is greatly modified by the 
circumstances in which the body is placed. Thus, cold 

itlv increases the quantity of air which is breathed, 
the quantity of oxygen absorbed, and of carbonic acid ex- 
pelled ; exercise and the taking of Too I have a correspond- 
ing effect 

In proportion to the weight of the body, the activity 

1 Tin l-'-riment. 



118 ELEMENTARY PHYSIOLOGY. 

of the respiratory process is far greatest in children, and 
diminishes gradually with age. The excretion of carbonic 
acid is greatest during the day, and gradually sinks at night, 
attaining its minimum about midnight, or a little after. 

Recent observations appear to show that the rule, that 
the quantity of oxygen taken in by respiration is, approxi- 
mately, equal to that given out by expiration, only holds 
good for the total result of tw T enty-four hours' respiration. 
Much more oxygen appears to be given out during the 
daytime (in combination with carbon as carbonic acid) 
than is absorbed ; while, at night, much more oxygen is 
absorbed than is excreted as carbonic acid during the same 
period. And it is very probable that the deficiency of 
oxygen towards the end of the waking hours, which is 
thus produced, is one cause of the sense of fatigue which 
comes on at that time. This difference between day and 
night is, however, not constant, and appears to depend a 
good deal on the time when food is taken. 

The quantity of oxygen which disappears, in proportion 
to the carbonic acid given out, is greatest in carnivorous, 
least in herbivorous animals — greater in a man living on 
a flesh diet, than when the same man is feeding on vege- 
table matters. 

124. Asphyxia. — When a man is strangled, drowned, 
or choked, or is, in any other way, prevented from inspir- 
ing or expiring sufficiently pure atmospheric air, what is 
called asphyxia comes on. He grows "black in the face;" 
the veins become turgid; insensibility, not unfrequently 
accompanied by convulsive movements, sets in, and he is 
dead in a few minutes. 

But, in this asphyxiating process, two deadly influences 
of a distinct nature are cooperating ; one is the deprivation 
of oxygen, the other is the excessive accumulation of car- 
bonic acid in the blood. Oxygen starvation and carbonic- 
acid poisoning, each of which may be fatal in itself, are at 
work together. 



EFFECTS OF RESPIRATION. 119 

The effects of oxygen starvation may be studied sepa- 
rately, by placing a small animal under the receiver of an 
air-pump and exhausting the air; or by replacing the air 
by a stream of hydrogen or nitrogen gas. In these cases 
no accumulation of carbonic acid is permitted, but, on the 
other hand, the supply of oxygen soon becomes insufficient, 
and the animal quickly dies. And if the experiment be 
made in another way, by placing a small mammal, or bird, 
in air from which the carbonic acid is removed as soon as 
it is formed, the animal will nevertheless die as soon as 
the amount of oxygen is reduced to ten per cent, or there- 
abouts. 

The directly poisonous effect of carbonic acid, on the 
other hand, has been very much exaggerated. A very 
largo quantity of pure carbonic acid (ten to fifteen or 
twenty per cent.) may be contained in air, without pro- 
ducing any very serious immediate effect, if the quantity 
of oxygen be simultaneously increased. And it is possible 
that what appear to be the directly poisonous effects of 
carbonic acid may really arise from its taking up the room 
that ought to be occupied by oxygen. If this be the case, 
carbonic acid is a negative rather than a positive poison. 

125. How it destroys Life, — Whichever may be the 
more potent agency, the effect of the two, as combined in 
asphyxia, is to produce an obstruction, firstly, in the pul- 
monary circulation, and, secondly, in the veins of the body 
generally. The lungs and the right side of the heart, con- 
sequently, become gorged with blood, while the arteries 
and left side of the heart gradually empty themselves of 
the small supply of dark and unaerated blood which they 
receive. The heart becomes paralyzed, partly by reason 
of the distention of it< right side, bui chiefly from being 
supplied with venous blood; and all the organs of the body 
gradually cease to act. 

126. Poisoning by Sulphuretted Hydrogen and Carbonic 
Oxide. — Sulphuretted hydrogen, so well known by its of- 



120 ELEMENTARY PHYSIOLOGY. 

fensive smell, has long had the repute of being a positive 
poison. But its evil effects appear to arise chiefly, if not 
wholly, from the circumstance that its hydrogen combines 
with the oxygen carried by the blood-corpuscles, and thus 
gives rise, indirectly, to a form of oxygen starvation. 

Carbonic-oxide gas has a much more serious effect, as it 
turns out the oxygen from the blood-corpuscles, and forms 
a combination of its own with the haemoglobin. The com- 
pound thus formed is only very gradually decomposed by 
fresh oxygen, so that if any large proportion of the blood- 
corpuscles be thus rendered useless, the animal dies before 
restoration can be effected. 

Badly-made common gas sometimes contains twenty to 
thirty per cent, of carbonic oxide ; and, under these circum- 
stances, a leakage of the pipes in a house may be extremely 
perilous to life. 

127. Slow Asphyxiation. — It is not necessary, however, 
absolutely to strangle, or drown, a man, in order to as- 
phyxiate him. As, other things being alike, the rapidity 
of diffusion between two gaseous mixtures depends on the 
difference of the proportions in which their constituents are 
mixed, it follows that the more nearly the composition of 
the tidal air approaches that of the stationary air, the slower 
will be the diffusion of carbonic acid outwards and of oxy- 
gen inwards, and the more charged with carbonic acid and 
defective in oxygen will the air in the air-cells become. 
And, on diminishing the proportion of oxygen or increas- 
ing the proportion of carbonic acid in the tidal air, a point 
will at length be reached when the change effected in the 
stationary air is too slight to enable it to relieve the pul- 
monary blood of its carbonic acid, and to supply it with 
oxygen to the extent required for its arterialization. In 
this case the blood, which passes into the aorta, and is 
thence distributed to the heart and the body generally, 
being venous, all the symptoms of insensibility, loss of 
muscular power, and the like, which have been enumerated 



SOURCES OF LOSS TO THE BLOOD. 121 

above as the results of supplying the brain and muscles 
with venous blood, will follow, and a stage of suffocation, 
or asphyxia, will supervene. 

Asphyxia takes place whenever the proportion of car- 
bonic acid in tidal air reaches ton per cent, (the oxygen 
being diminished in like proportion). And it makes no 
difference whether tins condition of the tidal air is brought 
about by shutting out fresh air, or by augmenting the num- 
ber of persons who are consuming the same air; or by 
suffering combustion, in any shape, to carry off oxygen 
from fche air. 

128. Vital Necessity of Ventilation. — But the depriva- 
tion of oxygon, and the accumulation of carbonic acid, cause 
injury long before the asphyxiating point is reached. Un- 
3S and headache arise when loss than one per cent. 
of fche oxygon of the air is replaced by other matters; while 
the persistent breathing of such air tends to lower all kinds 
of vital energy, and predisposes to disease. 

Hence the necessity of sufficient air, and of ventilation 
for every human being. To be supplied with respiratory 
air in a fair state of purity, every man ought to have at 
l«;i-t eight hundred cubic feet of space 1 to himself, and 
that space ought to be freely accessible, by direct or indi- 
rect channels, to the atmosphere. 



CHAPTER V. 

Tin: ><>ri;< ES OF LOSS A\D of GAIN To THE BLOOD. 

>!.< now I. — Sources of Loss to the Blood. 

129. Distribution of Arterial Blood. — The blood which 
ha- been aerated, or arterialized, by the process described 

ibfcaJ room ninr- feet hiirh. wide, ind long, contain- only s<v.n hundred .in I 
hrentr-nini I air. 



122 ELEMENTARY PHYSIOLOGY. 

in the preceding chapter, is carried from the lungs by the 
pulmonary veins to the left auricle, and is then forced by 
the auricle into the ventricle, and by the ventricle into the 
aorta. As that great vessel traverses the thorax, it gives 
off several large arteries, by means of which blood is dis- 
tributed to the head, the arms, and the walls of the body. 
Passing through the diaphragm (Fig. 29), the aortic trunk 
enters the cavity of the abdomen, and becomes what is 
called the abdominal aorta, from which vessels are given 
off to the viscera of the abdomen. Finally, the main stream 
of blood flows into the iliac arteries, whence the viscera of 
the pelvis and the legs are supplied. 

Having traversed the ultimate ramifications of the ar- 
teries, the blood, as we have seen, enters the capillaries. 
Here the products of the waste of the tissues constantly 
pour into it ; and, as the blood is everywhere full of cor- 
puscles, which, like all other living things, decay and die, 
the results of their decomposition everywhere accumulate 
in it. It follows that, if the blood is to be kept pure, the 
waste matters thus incessantly poured into, or generated in 
it, must be as constantly got rid of, or excreted. 

130. The Various Drains upon the Blood. — Three dis- 
tinct sets of organs are especially charged with this office 
of continually excreting carbonic acid, water, and urea. 
They are the lungs, the kidneys, and the skin (see 28). 
These three great organs may therefore be regarded as so 
many drains from the blood — as so many channels by which 
it is constantly losing substance. 

Further, the blood, as it passes through the capillaries, 
is constantly losing matter by exudation into the surround- 
ing tissues. 

Another kind of loss takes place from the surface of the 
body generally, and from the interior of the air-passages 
and lungs. Heat is constantly being given off from the 
former by radiation, evaporation, and conduction : from the 
latter, chiefly by evaporation. 



SOURCES OF LOSS TO THE BLOOD. 123 

131. Loss by the Liver and Lungs. — The blood which 
enters the liver is constantly losing material to that or 
-an; but the loss is only temporary, as almost all the 
matter lost, converted into sugar and into bile, reenters 
the current of the circulation in the liver itself, or else* 
where. 

Again, the loss of matter by the lungs in expiration is 
partially made pod by the no less constant gain which 
results from the quantity ^( oxygen absorbed at each, in- 
spiration: while the combustion which is carried on in the 
tissues, by means <^( this oxygen, is the source not only of 
the heat which is given off through the lungs, but also of 
that which is carried away from the general surface of the 

I v. And the loss by exudation from the capillaries is, 
in some degree, compensated by the gain from the lym- 
phatics and ductless glands. 

132. Other Losses and Gains. — In the instances just 
mentioned the loss and gain are constant, and go on while 
life and health last. Bui there are certain other operations 
which cause either loss or gain to the blood, and which are 
not continuous, but take place at intervals. 

These are. on the side of loss, the actions of the many 
retory glands^ which separate certain substances from 
the blood at recurrent periods, in the intervals of which 
they are quiescent. 

On the side of gain are the contractions of the mus- 
cles, which, during their activity, cause a great quantity 
of waste materials to appear in the blood; and the opera- 
tions of the alimentary canal, which, for a certain period 
after food has been taken, pour new materials into the 
blood. 

I nder some circumstances, the skin, by absorbing fluids, 
ma v become a source of gain. 

133. Table of Sources of Loss and Gain. — Tim sources 
of loss and gain to the blood may be conveniently arranged 
in the following tabular form : 



124 ELEMENTARY PHYSIOLOGY. 

A. Incessantly Active Sources of Loss or Gain to 

the Blood. 1 

a. Sources of loss. 

I. Loss of Matter. 

1. The lungs (carbonic acid, water). 

2. The kidneys (urea, water, salines). 

3. The skin (water, carbonic acid). 

4. The liver (bile, glycogen). 

5. The tissues generally (constructive material). 
II. Loss of heat. 

1. The free surfaces of the body. 

b. Sources of gain. 

I. Gain of matter. 

1. The lungs (oxygen). 

2. The liver (sugar, etc.). 

3. The lymphatics (corpuscles, lymph). 

4. The tissues generally (waste matters). 

5. The spleen and other ductless glands. 
II. Gain of heat. 

1. The blood itself and the tissues generally. 

B. Intermittently Active Sources of Loss or Gain 

to the Blood. 

a. Sources of loss. 

1. Many secreting glands (secretions). 

b. Sources of gain. 

1. The muscles (waste matters). 

2. The alimentary canal (food). 

The skin (absorption of liquids occasionally). 

134. Constant Loss by the Kidneys. — In the preceding 
chapter I have described the operation by which the lungs 

1 The learner must be careful not to confound the losses and gains of the blood 
with the losses and gains of the body as a whole. The two differ in much the same 
way as the internal commerce of a country differs from its export and import trade. 



SOURCES OF LOSS TO THE BLOOD. 125 

withdraw from the blood much carbonic acid and water, 
and supply oxygen to the blood; I now proceed to the 
second source of continual loss, the KlDNEYS. 

Of these organs, there are two, placed at the back of 
the abdominal cavity, one on each side of the lumbar re- 
gion of the spine. Each, though somewhat Larger than the 
kidney of a sheep, has a similar shape. The depressed, or 
concave, side of the kidney is turned inwards, or towards 
the spine ; and its convex side is directed outwards (Fig, 
32). From the middle of the concave side (called the 
hiltis) of each kidney, a long tube with a small bore, the 
Ureter (Cv\), proceeds to the Bladder (BL). 



rrn 




Fig 82. 

The kidneys ( A". »: ureters ( f'r.): with the aorta (Ao.), and vena c a va inferior ( V. 
: and th< : renal arteries and veins. Bl. is the bladder, the top of which is cut off 
so aa to show the openings of the ureters {\. i», and that of the urethra 

The latter, situated in the pelvis. IS an oval bag, the 

walls of which contain abundant unstriped muscular fibre, 
while it is lined, internally, by mucous membrane, and 
coated externally by a layer of the peritoneum, or double 

hair of BerOUS membrane which has exactly the same rehe 

tions to the cavity of the abdomen and the viscera con- 



126 ELEMENTARY PHYSIOLOGY. 

tained in them as the pleura have to the thoracic cavity 
and the lungs. The ureters open side by side, but at some 
little distance from one another, on the posterior and in- 
ferior wall of the bladder (Fig. 32, 1, 1). In front of them 
is a single aperture which leads into the canal called the 
Urethra (Fig. 32, 2), by which the cavity of the bladder is 
placed in communication with the exterior of the body. 
The openings of the ureters enter the walls of the bladder 
obliquely, so that it is much more easy for ihe fluid to pass 
from the ureters into the bladder than for it to get the 
other way, from the bladder into the ureters. 

Mechanically speaking, there is little obstacle to the 
free flow of fluid from the ureters into the bladder, and 
from the bladder into the urethra, and so outwards ; but 
certain muscular fibres arranged circularly around the part 
called the " neck " of the bladder, where it joins the ure- 
thra, constitute what is termed a sphincter, and are usually, 
during life, in a state of contraction, so as to close the exit 
of the bladder, while the other muscular fibres of the organ 
are relaxed. 

It is only at intervals that this state of matters is re- 
versed ; and the walls of the bladder contracting, while its 
sphincter relaxes, its contents, the urine, are discharged. 
But, though the expulsion of the secretion of the kidneys 
from the body is thus intermittent, the excretion itself is 
constant, and the urinary fluid flows, drop by drop, from 
the opening of the ureters into the bladder. Here it ac- 
cumulates, until its quantity is sufficient to give rise to the 
uneasy sensations which compel its expulsion. 

135. Composition of Renal Excretion.— The renal excre- 
tion has naturally an acid reaction, and consists chiefly of 
urea with some uric acid, sundry other animal products 
of less importance, including certain coloring-matters, and 
saline and gaseous substances, all held in solution by a 
large quantity of water. 

The quantity and composition of the urine vary greatly 



SOURCES OF LOSS TO THE BLOOD. 127 

according to the time of day ; the temperature and moist- 
ure of the air; the fasting or replete condition of the 
alimentary canal ; and the nature of the food. 

Urea and uric acid are both composed of the elements 
carbon, hydrogen, oxygen, and nitrogen; but the urea is 
by far the more soluble in water, and greatly exceeds the 
uric acid in quantity. 

An average healthy man excretes by the kidneys about 
fifty (nines, or twenty-four thousand grains of water a day. 
In this are dissolved five hundred grains of urea, but not 
more than ten to twelve grains of uric acid. 

The amount of other animal matters, and of saline sub- 
stances, varies from one-third as much to nearly the same 
amount as the urea. The saline matters consist chiefly of 
common salt, phosphates and sulphates of potash, soda, 
lime, and magnesia. The gases are the same as those in 
the blood — namely, carbonic acid, oxygen, and nitrogen. 
Hut the quantity is, proportionally, less than one-third as 
groat ; and the carbonic acid is in very large, while the 

gen is in very small, amount. 

The average specific gravity docs not differ very widely 
from that of blood-serum, being 1.020. 

136. Kidneys and Lungs compared. — The excretion of 
nitrogenous waste and water, with a little carbonic acid, 
by the kidneys, is thus strictly comparable to that of car- 
bonic arid and water, by the lungs, in the air-cells of w r hich 
carbonic acid and watery vapors are incessantly accumu- 
lating, to be periodically expelled by the act of expiration. 
Bui the operation of the renal apparatus differs from thai 
of the respiratory organs, in the far longer intervals be- 
tween the expulsory acts ; and still more in the circum- 

QCe that, while the substance which the lungs take into 

the body is as important a> those which they give out, the 

kidney- take in nothing. 

137. The Structure of the Kidney.— It will be observed 

that all the chief Constituents of the urine are already con- 



128 



ELEMENTARY PHYSIOLOGY. 



tained in the blood, and indeed, it might almost be said to 
be the blood devoid of its corpuscles, fibrin, and albumen. 
Speaking broadly, it is such a fluid as might be separated 
from the blood by the help of any kind of filter which had 
the property of retaining these constituents, and letting 
the rest flow off. The filter required is found in the kid- 
ney, with the minute structure of which it is now neces- 
sary to become acquainted. 

When a longitudinal section of a kidney is made (Fig. 
33), the upper end of the ureter ( U) seems to widen out 




Fig. 83. 
Longitudinal Section of the Human Kidney. 

Ct., the cortical substance ; J/., the medullary substance ; P., the pelvis of the kid- 
ney; £7., the ureter; R.A., the renal artery. 



into a basin-like cavity (P), which is called the pelvis of 
the kidney. Into this, sundry conical elevations, called the 
pyramids {Py) project ; and their summits present mul- 
titudes of minute openings — the final terminations of the 
tubulin of which the thickness of the kidnev is chiefly 



SOURCES OF LOSS TO THE BLOOD. 



129 



made up. If the tubules be traced from their openings 
towards the outer surface, they are found, at first, to lie 
parallel with one another in bundles, which radiate tow- 
ards the surface, and subdivide as they go; but at length 
they spread about irregularly, and become interlaced. From 
this circumstance, the middle, or medullary, part (marrow, 
duUa) of the kidney looks different from the superficial 




Fr... 84. 

Diagrammatic View of the Course of the Tubules in the Kidney. 

r. eortfcal portion troweling to CI in Fig. 88, k being close to the surface of the 
kidneys : (/. p. medullary portion, p reaching to the- summit of the pyramid. IX, 
opening of tubule on the pyramid; VI II. VII PZ the straight portion of the tu- 
V— II. the twisted portion of the tubules: /. the Bialpignian capsule. 

or cortical, part (bark, cortex) ; but, in addition, the cor- 
tical part i*> more abundantly supplied with vessels than 
the medullary, and hence has a darker aspect. The great 
majority of the tubules, after- a very devious course, ulti- 
mately terminate in dilatations (Fig. 35) 3 which are called 
Malpighian capsules. Into the summit of each capsule a 
small vessel (Figs. 35 mid 36, pa), one of the ultimate 



130 



ELEMENTARY PHYSIOLOGY. 



branches of the renal artery (Fig. 33, RA\ enters (driving 
the thin wall of the capsule before it), and immediately 
breaks up into a bunch of looped capillaries, called a glo- 
merulus (Fig. 35, gl), which nearly fills the cavity of the 




Fig. 85. 

A Malpigihan Capsule highly magnified. 

to, small branch of renal artery entering the capsule, breaking up into the glomeru- 
lus, ql and finally joining again to form the vein. ve. <•. the tubule ; </, the epithelium 
over the glomerulus; b, the epithelium lining the capsule. 




Fig. 36. 

Circulation en the Kidney. 

at, small branch of renal artery giving off the branch ret. which enters glomerulus, 
issues as re. and then breaks up into capillaries, which, after surrounding the tubule, 
find their way by r into W. branch of the renal vein ; m. capillaries around tubules in 
parts of the cortical substance where there are no glomeruli. 



SOURCES OF LOSS TO THE BLOOD. 131 

capsule. The blood is carried a way from this glomerulus 
by a small vein (ve), which does not, at once, join with 
other veins into a larger venous trunk, but opens into the 
net-work of capillaries (Fig. 36) which surrounds the tu- 
bule, thus repeating the portal circulation on a small scale. 

The tubule has an epithelial lining (Fig. 35, C, and Fig. 
37, 'M. continuous with that of the pelvis of the kidney, 
and the urinary passages generally. The epithelium is 
thick and plain enough in the tubule, but it becomes very 
delicate, or even disappears, in the capsule and on the 
glomerulus (Fig. 35, rt, b). 

138. The Filtering Mechanism, — It is obvious, from 
this description, that the surface of the glomerulus is, 
practically, free, or in direct communication with the ex- 
terior by means of the cavity of the tubule; and further, 
that, in each vessel of the glomerulus, a thin stream of 
blood constantly Hows, only separated from the cavity of 
the tubule by the vevy delicate membrane of which the 




Fig. 37. 

Tbambybsi Sf.< tiun ok Two Tubules. 

a a. canals of tubules surrounded by their epithelium, h. a blood-vessel cut across. 

wall of the vessel is composed. The Malpigbian capsule 
may, in fact, be regarded as a funnel, and the membranous 
walls of the glomerulus as a piece of very delicate filtering- 
paper, into which the blood is poured. 

139. Changes of the Blood while passing through the 

Kidneys. — The blood which supplies the kidneys is brought 
directly from the aorta by the renal arteries, so that it has 



132 ELEMENTARY PHYSIOLOGY. 

but shortly left the heart. The venous blood which enters 
the heart, and is propelled to the lungs, charged with the 
nitrogenous, as w^ell as with the other products of waste, 
loses only an inappreciable quantity of the former in its 
course through the lungs ; so that the arterial blood which 
fills the aorta is pure only as regards carbonaceous waste, 
while it is impure as regards urea and uric acid. 

In the healthy condition, the walls of the minute renal 
arteries and veins are relaxed, so that the passage of the 
blood is very free ; and but little waste, arising from mus- 
cular contraction in the walls of these vessels, is thrown 
into the renal blood. And, as the urine which is separated 
from the renal blood contains proportionately less oxygen 
and more carbonic acid than the blood itself, any gain of 
carbonic acid from this source is probably at once counter- 
balanced. Hence, so long as the kidney is performing its 
functions properly, the blood which leaves the organ by 
the renal vein is as bright scarlet as that which enters it 
by the renal artery. Strictly speaking, it is the purest 
blood in the body, careful analysis having shown that it 
contains a sensibly smaller quantity of urea and of water 
than that of the left side of the heart. This difference is, 
of course, a necessary result of the excretion of the urinary 
fluid from the blood as it travels through the kidney. 

As the renal veins pour their contents directly into the 
inferior vena cava (see Fig. 32), it follows that the blood in 
the upper part of this vein is so much the less impure, or 
venous, than that contained in the inferior vena cava, below 
the renal veins. 

140. The Nervous System controls the Renal Excretion. 
— Irritation of the nerves which supply the walls of the 
vessels of the kidney has the immediate effect of stopping 
the excretion of urine, and rendering the renal blood dark 
and venous. The first effect would appear to be explicable 
by the diminution of the pressure exerted upon the blood 
in the Malpighian tufts, in consequence of the diminution 



SOURCES OF LOSS TO THE BLOOD. 133 

in the size of the channels — the small arteries — by which 
the blood reaches them. And the second effect is prob- 
ably, in part, a secondary result of the first — the excretion 
of carbonic acid by the urine ceasing with the suppress^ n 
o{ that fluid ; while, to a largo extent, it is also the result 
of a pouring in of carbonic acid into the renal blood, in 
consequence i)( the work of the muscles of the small ves- 
sels, and the waste which results therefrom, 

141. The Loss by the Skin.— That the skin is a source 
of continual loss to the blood may be proved in various 
ways. If the whole body of a man, or one of his limbs, be 
inclosed in a caoutchouc bag, full of air, it will be found 
that this air undergoes changes which are similar in kind 
to those which take place in the air which is inspired into 
the lunjjs. That is to say, the air loses oxygen and gains 
carbonic acid ; it also receives a great quantity of watery 
vapor, which condenses upon* the sides of the bag, and 
may be drawn off by a properly-disposed pipe. 

Under ordinary circumstances no liquid water appears 
upon the surface of the integument, and the whole process 
receives the name of the insensible perspircftio?i. But, 
when violent exercise is taken, or under some kinds of 
mental emotion, or when the body is exposed to a hot and 
moist atmosphere, the perspiration becomes sensible ; thai 
is, appears in the form of scattered drops upon the surface. 

142. Quantity of the Cutaneous Excretions. — Thequan- 
tity of sirf<tt % or sensible perspiration, and also the total 
amount of both sensible and insensible perspiration, vary 
immensely, according to the temperature and oilier con 
ditions of the air, and according to the state of the blood 
Mud of the nervous system. It is estimated that, as «*i gen- 
eral rule, the quantity of water excreted by the skin is 
about double that given out by the lungs in the same time. 
The quantity of carbonic acid is not above .^.ili or /jh of 
that excreted by the lungs; and it is not certain that in 
health any apprt *iabh quantity of urea is given of]". 



134 ELEMENTARY PHYSIOLOGY. 

In its normal state the sweat is acid, and contains fatty 
matters, even when obtained free from the fatty products 
of the sebaceous glands. Ordinarily, perspiration, as it 
collects upon the skin, is mixed with the fatty secretion 
of these glands ; and, in addition, contains scales of the 
external layers of the epidermis, which are constantly 
being shed. 

143. Perspiration by Simple Transudation. — In analyz- 
ing the process by which the perspiration is eliminated 
from the body, it must be recollected, in the first place, 
that the skin, even if there were no glandular structures 
connected with it, would be in the position of a moderately 
thick, permeable membrane, interposed between a hot fluid, 
the blood, and the atmosphere. Even in hot climates the 
air is, usually, far from being completely saturated with 
watery vapor, and in temperate climates it ceases to be so 
saturated the moment it comes into contact with the skin, 
the temperature of which is, ordinarily, twenty or thirty 
degrees above its own. 

A bladder exhibits no sensible pores, but, if filled with 
water and suspended in the air, the water will gradually 
ooze through the walls of the bladder, and disappear by 
evaporation. Now, in its relation to the blood, the skin is 
such a bladder full of hot fluid. 

Thus, perspiration to a certain amount must always be 
going on through the substance of the integument ; but 
what the amount of this perspiration may be cannot be 
accurately ascertained, because a second and very impor- 
tant source of the perspiration is to be found in what are 
called the sweat-glands. 

144. The Sweat-Glands. — Ail over the body the integu- 
ment presents minute apertures, the ends of channels exca- 
vated in the epidermis or scarf-skin, and each continuing the 
direction of a minute tube, usually about 3^o"th of an inch 
in diameter, and a quarter of an inch long, which is em- 
bedded in the dermis. Each tube is lined with an epithe- 



SOURCES OF LOSS TO THE BLOOD. 



135 



Hum continuous with the epidermis (Fig. 40, e). The tube 
sometimes divides, but, whether single or branched, its 
inner end or ends are blind, and coiled up into a sort of 
knot, interlaced with a mesh-work of capillaries (Fig 38, #, 
and Fig. 41). 

The blood in these capillaries is therefore separated 
from the cavity of the sweat-gland only by the thin walls 
of the capillaries, that of the glandular tube, and its epi- 
thelium, which, taken together, constitute but a very thin 
pellicle ; and the arrangement, though different in detail, 




^ f 





Fn;. 80. 

Fig. 8S. — Section of th<- skin showing the sweat-glands, a. the epidermis ; h. its 
deeper layer, the reie MalpighH; a, cf, the dermis or true skin ; f y nit-cells ; (/. the 

eat-gbna : />. its duct : >'. its opening on the surface of the epider 

m of the skin showing 'he root* of the hairs and the sebaceous 
i. b. muscle of c, the hair-sheath, on the left hand. 



is similar in principle to that which obtains in the kidney. 
In the latter, the vessel makes a coil within the Blalpighian 
capsule, which end- a tubule. Here the perspiratory tubule 
coils about and among the vessels. In both cases the same 
result is arrived at — namely, the exposure oi the blood to 
■ large, relatively free, surface, on to which certain of its 
tents transude. 



136 



ELEMENTARY PHYSIOLOGY. 



The number of these glands varies in different parts of 
the body. They are fewest in the back and neck, where 
their number is not much more than four hundred to a 
square inch. They are more numerous on the skin of the 
palm and sole, where their apertures follow the ridges 
visible on the skin, and amount to between two and three 




Fig. 40. 
Portion of Fi°\ 38 more highly magnified— somewhat diagrammatic, a horny 
epidermis; &, softer layer, rete Malpighii ; c, dermis; d, lowermost vertical layer ot 
epidermic cells ; e, cells lining the sweat-duct continuous with epidermic cells ; n. 
corkscrew canal of sweat-duct. To the right of the sweat-duct the dermis is raised 
into a papilla, in which the small artery,/, breaks up into capillaries, ultimately torm- 
ing the veins, g. 



SOURCES OF LOSS TO THE BLOOD. 



13, 



thousand on the square inch. At a rough estimate, the 
whole integument probably possesses not fewer than from 
two millions and a quarter to two millions and a half of 
these tubules, which therefore must possess a very great 
aggregate secreting power. 




Fig. 41. 

Coiled end of a >\veat-srland (Fig. 88, g). epithelium not shown, a. the coil; b. the 
duet: c. net-work of capillaries. Inside which the duct-gland lies. 



145. These Glands are controlled by the Nervous Sys- 
tem, — The sweat-glands are greatly under the influence of 
the nervous system. This is proved, not merely by the 
well-known effects of mental emotion in sometimes sup- 
pressing the perspiration and sometimes causing it to be 
poured forth in immense abundance, but has been made a 
matter of direct experiment. There are some animals, such 

the horse, which perspire very freely. If the sympa- 
thetic in rve of one side, in the neck of a horse, be cut, tlie 

tie side of the head becomes injected with blood, and 
it- temperature rises (67); and, simultaneously, sweat is 
poured out abundantly over the whole Burface thus affect- 



138 ELEMENTAKY PHYSIOLOGY. 

ed. On irritating that end of the cut nerve which is in 
connection with the vessels, the muscular walls of the lat- 
ter, to which the nerve is distributed, contract, the conges- 
tion ceases, and with it the perspiration. 

146. Variations in the Perspiratory Losses. — The amount 
of matter which may be lost by perspiration, under certain 
circumstances, is very remarkable. Heat and severe labor, 
combined, may reduce the weight of a man two or three 
pounds in an hour, by means of the cutaneous perspiration 
alone ; and, as there is some reason to believe that the 
quantity of solid matter carried off from the blood does not 
diminish with the increase of the amount of the perspira- 
tion, the total amount of solids which are eliminated by 
profuse sweating may be considerable. 

The difference between blood which is coming from, 
and that which is going to, the skin, can only be con- 
cluded from the nature of the substances given out in the 
perspiration ; but arterial blood is not rendered venous in 
the skin. 

147. The Lungs, Skin, and Kidneys, compared.— It will 
now be instructive to compare together, in more detail 
than has been done in the first chapter (28), the three 
great organs — lungs, kidneys, and skin — which have been 
described. 

In ultimate anatomical analysis, each of these organs 
consists of a moist animal membrane separating the blood 
from the atmosphere. 

Water, carbonic acid, and solid matter, pass out from 
the blood through the animal membrane in each organ, and 
constitute its secretion or excretion ; but the three organs 
differ in the absolute and relative amounts of the constit- 
uents the escape of which they permit. 

Taken by weight, water is the predominant excretion 
in all three : most solid matter is given off by the kidneys ; 
most gaseous matter by the lungs. 

The skin partakes of the nature of both lungs and kid- 



LOSSES AND GAINS BY THE LIVER. 139 

neys, seeing that it absorbs oxygen and exhales carbonic 
acid and water, like the former, while it excretes organic 
and saline matter in solution, like the latter; but the skin 
is more closely related to the kidneys than to the lungs. 
Hence, when the free action of the skin is interrupted, its 
work is usually thrown upon the kidneys, and vice versa. 
In hot weather, when the excretion by the skin increases, 
that of the kidneys diminishes, and the reverse is observed 
in cold weather. 

This power of mutual substitution, however, only goes 
a little way ; for, if the kidneys be extirpated, or their 
functions much interfered with, death ensues, however ac- 
tive the skin may be. And, on the other hand, if the skin 
he covered with an impenetrable varnish, the temperature 
of the body rapidly falls, and death takes place, though the 
lungs and kidneys remain active. 

Sectiox II. — Losses and Gains by the Liver. 

148. Structure and Connections of the Liver. — The liver 
is a constant source both of loss, and, in a sense, of gain, 
to the blood which passes through it. It gives rise to 
loss, because it separates a peculiar fluid, the bile, from the 
blood, and throws that fluid into the intestine. It is also 
in another way a source of loss because it elaborates from 
the blood passing through it a substance called glycogen, 
which is stored up sometimes in large, sometimes in small, 
quantities in the cells cf the liver. This latter loss, how- 

r, is only temporary, and may be sooner or later con- 
verted into a gain, for this glycogen very readily passes 
into Sugar, and either in that form or in some other way is 
carried off by the blood. In this respect, therefore, there 
l- ;i gain to the blood of kind or quality, though not of 
quantity, of material. Finally, it is very probable that 
the liver is one source of the colorless corpuscles of the 
blood. 

The liver is the largesl glandular organ in the body. 



140 ELEMENTARY PHYSIOLOGY. 

ordinarily weighing about fifty or sixty ounces. It is a 
broad, dark, red-colored organ, which lies on the right side 
of the body, immediately below the diaphragm, with which 
its upper surface is in contact, while its lower surface 
touches the intestines and the right kidney. 




Fig. 48. 

The Liver turned fp and viewed from below. 

rt, vena cava; &, vena porta?; c, bile-duct : '/.hepatic artery; /.pall-bladder. The 
termination of the hepatic vein in the vena cava is not seen, being covered by the 
piece of the vena cava. 

The liver is invested by a coat of peritoneum, which 
keeps it in place. It is flattened from above downwards, 
and convex and smooth above, where it fits into the con- 
cavity of the lower surface of the diaphragm. Flat and 
irregular below (Fig. 42), it is thick behind, but ends in a 
thin edge in front. 

Viewed from below, as in Fig. 42, the inferior vena 
cava, a, is seen to traverse a notch in the hinder edge of 
the liver as it passes from the abdomen to the thorax. At 
b the trunk of the vena portce is observed dividing into the 
chief branches which enter into, and ramify through, the 
substance of the organ. At d, the hepatic artery, coming 
almost directly from the aorta, similarly divides, enters the 
liver, and ramifies through it ; while at c is the single 
trunk of the duct, called the hepatic duct, which conveys 
away the bile brought to it by its right and left branches 



LOSSES AND GAINS BY THE LIVER. 



141 



from the liver. Opening into the hepatic duct is seen the 
duct of a large oval sac, /, the gall-bladder. The duct is 
smaller than the artery, and the artery than the portal 
vein. 

If the branches of the artery, the portal vein, and the 
bile-duct, be traced into the substance of the liver, they 
will be found to accompany one another, and to branch out 
and subdivide, becoming smaller and smaller. At length 



JTK\ 




Fio. 48. 

A section of part of the liver to show //. I'.. ;i branch of the hepatic- vein, with L., 
the lobules or acini of the liver, seated uj>oii its walls, and sending their intralobular 
Teins into it. 



the portal vein and hepatic artery (Wig. 45, ^\P.) will be 
found to end in the capillaries, which traverse, like a net- 
work, the substance of the smallest obvious subdivisions 
of the liver-substance — polygonal masses of one-tenth of 

an inch in diameter, Or less, which are termed the lobftlis. 

Every lobuL is seated by its base upon one of the ramifica- 



142 



ELEMENTARY PHYSIOLOGY. 



tions of a great vein — the hepatic vein — and the blood of 
the capillaries of the lobule is poured into that vein by a 
minute veinlet, called intralobular (Fig. 45, H. K), which 
traverses the centre of the lobule, and pierces its base. 
Thus the venous blood of the portal vein and the arterial 
blood of the hepatic artery reach the surfaces of the lobules 
by the ultimate ramifications of that vein and artery, be- 
come mixed in the capillaries of each lobule, and are car- 
ried off by its intralobular veinlet, which pours its contents 
into one of the ramifications of the hepatic vein. These 
ramifications, joining together, form larger and larger 
trunks, which at length reach the hinder margin of the 
liver, and finally open into the vena cava inferior, where 
it passes upwards in contact with that part of the organ. 

Thus the blood with which the liver is supplied is a 
mixture of arterial and venous blood ; the former brought 




a, ultimate branches of the hepatic duct; b, liver-cells. 



by the hepatic artery directly from the aorta, the latter by 
the portal vein from the capillaries of the stomach, intes- 
tines, pancreas, and spleen. 

What ultimately becomes of the ramifications of the 
hepatic duct is not certainly known. Lined by an epithe- 
lium, which is continuous with that of the main duct, and 
thence with that of the intestines, into which the main 



LOSSES AND GAINS BY THE LIVER. 



143 



duct opens, they may be traced to the very surface of the 
lobules. Their ultimate ramifications are not yet thor- 



Fig. 4o. 




wiBmMSi 



Fio. M, 

W\r.4& — Section of partially-injected liver magnified The artificial white line is 
Introduced to mark the limit> of a lobule. VI'.. branches of portal vein breaking up 

into capillaries, which run towards the centre of the lobule, and join //. ]'.. the Intra* 
lobolar branch of the hepatic vein. The outlines of the Irrer-ceus are seen as a fine 

•rk of lines throughout th«- whole lobule. 
V\'j. 4o. — Portion of lobule very highly magnified. ". liv.-r-eeil with ». oncleiu (two 
•i; &, capillaries cut acroea; c. minute biliary paaeagefl between the 
cells, injected with coloring-matter 



144 ELEMENTARY PHYSIOLOGY. 

oughly determined : but recent investigations tend to show 
that they communicate with minute passages left between 
the hepatic cells, and traversing the lobule in the intervals 
left by the capillaries (Fig. 46). However this may be, 
any fluid separated from the blood by the lobules must 
really find its way into them. 

In the lobules themselves all the meshes of the blood- 
vessels are occupied by the liver-cells. These are many- 
sided, minute bodies, each about y-oVo^h of an inch in 
diameter, possessing a nucleus in its interior, and fre- 
quently having larger and smaller granules of fatty matter 
distributed through its substance (Fig. 46, a). It is in 
the liver-cells that the active powers of the liver are sup- 
posed to reside. 

149. The Active Powers of the Liver-Cells. — The nature 
of these active powers, so far as the liver is a source of loss 
to the blood which traverses it, is determined by ascertain- 
ing— 

a. The character of that fluid, the bile, which inces- 
santly flows down the biliary duct, and which, if digestion 
is not going on, and the passage into the intestine is 
closed, flows back into and fills the gallbladder. 

b. The difference between the blood which enters the 
liver and that which leaves it. 

150. The Bile— its Quantity and Composition. — a. The to- 
tal quantity of bile secreted in the twenty-four hours varies, 
but probably amounts to not less than from two to three 
pounds. It is a golden-yellow, slightly alkaline fluid, of 
extremely bitter taste, consisting of water with from sev- 
enteen per cent, to half that quantity of solid matter in 
solution. The solids consist, in the first place, of a some- 
what complex substance which may be separated by crys- 
tallization, and has been called bilin. It is in reality a 
mixture of two acids, in combination with soda, one called 
glycocholic, and consisting of carbon, hydrogen, nitrogen, 
and oxygen, the other taarocholic^ and containing in addi- 



SOURCES OF (IAIN TO THE BLOOD. 145 

tion to the other elements a considerable quantity of sul- 
phur. Besides the taurocholate and glyoocholate of soda, 
or bile-salts as they are sometimes called, the bile contains 
a remarkable crystalline Bubstance, very Catty-looking, but 
not really of a fatty nature, called cholestertn, one or more 
peculiar coloring-matters probably related to the hsematin 
of the blood, and certain saline matters. 

h. ( tf these constituents of the bile, the water, the choles- 
terin, and the saline matters, alone, are discoverable in the 
blood ; and, though doubtless some difference obtains be- 
tween the blood which enters the liver and that which 
leaves it, in respect of the proportional quantity of these 
constituents, great practical difficulties lie in the way of 
the precise ascertainment of the amount of that difference. 
The blood of the hepatic vein, however, is certainly poorer 
in water than that of the portal vein. 

151. Bile is formed in the Liver-Cells. — As the essen- 
tial constituents of bile, the bile-acids and the coloring- 
matter are not discoverable in the blood which enters the 
liver; they must be formed at the expense of the tissue 
of that organ itself, or of some constituent of the blood 
passing through it. 

Section III. — Sources of Gain to the Blood. 

152. The Skin as an Organ of Respiration. — We must 
next consider the chief sources of constant gain to the 
blood ; and, in the first place, the sources of gain of 
matti r. 

The lungs and skin are, as has been seen, two of the 
principal channels by which the body Loses liquid and 
seous matter, but they are also the sole means by which 
one of the most important of all substances for the main- 
tenance of life, oxygen, i- introduced into the blood. It 
has already been pointed out that the volume of the oxy- 
gen taken into the blood by the lungs IS rather create? 
than that of the carbonic acid iriveii out. The absolute 
10 



146 ELEMENTARY PHYSIOLOGY. 

weight of oxygen thus absorbed may be estimated at ten 
thousand grains (see 165). 

How much is taken in by the skin of man is not cer- 
tainly known, but in some of the lower animals, such as 
the frog, the skin plays a very important part in the per- 
formance of the respiratory function. 

153. Reaction of the Liver upon the Blood. — The blood 
leaving the liver by the hepatic vein not only contains pro- 
portionally less water and fibrin, but proportionally more 
corpuscles, especially colorless corpuscles, and, what is 
still more important, under certain circumstances at least, 
a larger quantity of liver -sugar, or glucose, than that 
brought to it by the portal veins and hepatic artery. 

That the blood leaving the liver should contain propor- 
tionally less water and more corpuscles than that entering 
it, is no more than might be expected from the fact that the 
formation of the bile, which is separated from this blood, 
necessarily involves a loss of water and of some solid mat- 
ters, while it does not abstract any of the corpuscles. 

We do not know why less fibrin separates from the 
blood of the hepatic vein than from the blood brought to 
the liver. But the reason why there is always more sugar 
in the blood leaving the liver than in that entering it, and 
why, in fact, there may be plenty of sugar in the blood of 
the hepatic vein even when none whatever is brought to it 
by the hepatic artery, or portal vein, has been made out by 
careful and ingenious experimental research. 

154. Sugar-forming Function of the Liver. — If an ani- 
mal be fed upon purely animal food, the blood of the por- 
tal vein will contain no sugar, none having been absorbed 
by the walls of the alimentary canal, nor will that of the 
hepatic artery contain any, or, at any rate, more than the 
merest trace. Nevertheless, plenty will be found, at the 
same time, in the blood of the hepatic vein and in that of 
the vena cava, from the point at which it is joined by the 
hepatic vein, as far as the heart. 



SOURCES OF GAIN TO THE BLOOD. 147 

Secondly, it", from an animal so fed, the liver be ex- 
tracted, and a current of cold water forced into the vena 
porta*) it will flow out by the hepatic vein, carrying with 
it all the blood of the organ, and will, after a time, come 
out colorless, and devoid of sugar. Nevertheless, if the 
organ be left to itself at a moderate temperature, sugar 
will Boon again become abundant in it. 

Thirdly, from the liver, washed as above described, a 
substance may be extracted, by appropriate methods, which 
resembles starch or dextrine, in chemical composition, con- 
sisting as it docs of carbon united with hydrogen and oxy- 
gen, the latter being in the same proportions as in water. 
This "amyloid" substance is the glycogen spoken of in 
14S. It may be dried and kept for long periods without 
undergoing any change. 

But, like the vegetable starch and dextrine, this animal 
amyloid, which must be formed in the liver, since it is cer- 
tainly not contained either in the blood of the portal vein, 
cr in that of the hepatic artery, is very readily < -hanged, by 
contact with certain matters, which act as ferments, into 
gar. 

Fourthly, it may be demonstrated that a ferment, com- 
petent to change the "amyloid" glycogen into saccharine 
u glucose" exists under ordinary circumstances in the liver. 

Putting all these circumstances together, the following 

lanation of the riddle of the appearance of sugar in the 
blood of the hepatic vein and vena cava, when neither it, 
nor any compound Out of which it is easily formed, exists 
in the blood brought to the liver, appears to have much 

probability; though it may possibly require modification, 
in some respects, hereafter. 

The liver forms glycogen out ( f the blood with which it 

supplied. The Bame blood supplies the ferment which, 

;it the temperature of the body, very speedily converts 
the comparatively little Boluble glycogen into very soluble 
sugar; and this sugar is dissolved and carried away by 



148 ELEMENTARY PHYSIOLOGY. 

each intralobular vein to the hepatic vein, and thence to 
the vena cava. 

Though after death a very considerable quantity of sugar 
accumulates in the hepatic vein, the amount which, at any 
given moment, can be detected during life is extremely 
small. This has led some physiologists to suppose that, in 
health, glycogen is not converted into sugar, but undergoes 
some other change. A very small quantity of sugar, how- 
ever, so small as to almost escape detection, thrown into 
the hepatic vein every instant, would amount to a consid- 
erable quantity in the twenty-four hours. 

This formation of glycogen in the liver goes on in the 
total absence c_ starch or sugar from the food. It must, 
therefore, in such cases be formed at the expense of pro- 
teid materia] {see 176). It appears, however, that the 
presence of starch or sugar in the food, though not essen- 
tial, is very favorable to the production of glycogen in the 
liver. 

155. Gain by the Lymphatics. — The lymphatic system 
has been already mentioned as a feeder of the blood with 
a fluid which, in general, appears to be merely the super- 
fluous drainage, as it were, of the blood-vessels ; though at 
intervals, as we shall see, the lacteals make substantial 
additions of new matter. It is very probable that the 
multitudinous lymphatic glands may effect some change in 
the fluid which traverses them, or may add to the number 
of corpuscles in the lymph. 

Nothing certain is known of the functions of certain 
bodies w^hich are sometimes called ductless glands, but 
have quite a different structure from ordinary secreting 
glands ; and indeed do not resemble each other in struct- 
ure. These are, the thyroid gland, which' lies in the part 
of the throat below the larynx, and is that organ which, 
when enlarged by disease, gives rise to "Derbyshire neck" 
or " goitre ; " the thymus gland, situated at the base of the 
heart, largest in infants, and gradually disappearing in 



SOUR(T> OF GAIN TO THE BLOOD. 



149 



adult, or old, persons: and the SUptCHrenal capsules, which 
lie above the kidneys, 

156. The Spleen— its Functions unknown. — We are as 
much in the dark respecting the office of the large viscus 
called the spleen, which lies upon the left side of the 
stomach in the abdominal cavity (Kg. 47). It is an elon- 
gated flattened red body, abundantly supplied with blood 
by an artery called the splenic artery, which proceeds al- 
most directly from the aorta. The blood which has trav- 



VCT 



£J> 



J)m 



4F-B 




with the splenic artery (SpA. . Below this is seen the splenic 
vein runn . rm the vena porta | V.I'. . A .: I>.. ■ pillar of 

P. Ik. the pancreatic dn I 

- ■>.. the duodenum : B.I)., the biliary duct uniting with the pancr 
iiuon duct, x : y. the intestinal vesm 



the spleen is collected by the splenic vein, and is 
ried by it t<» the ^enaportOB, and so to the liver. 
A -<-ction of the spleen shows a dark-red spongy masfl 
dotted over with minute whitish spots. Kaeh of these la>t 
is t >f <.ii«- of the spheroidal bodies called cor- 

of the spleen, which are scattered thn ugfa ita sub- 
sist of a solid aL r L r reL r ation of minute 1m dies, 

like the white corpv the blood, traversed bya capil- 

lary net-work, which is fed by a small twig of the splenic 



150 ELEMENTARY PHYSIOLOGY. 

artery. The dark-red part of the spleen, in which these 
corpuscles are embedded, is composed of fibrous and elastic 
tissue supporting a very spongy vascular net-work. 

The elasticity of the splenic tissue allows the organ to 
be readily distended, and enables it to return to its former 
size after distention. It appears to change its dimensions 
with the state of the abdominal viscera, attaining its largest 
size about six hours after a full meal, and falling to its 
minimum bulk six or seven hours later, if no further sup- 
ply of food be taken. 

The blood of the splenic vein is found to contain pro- 
portionally fewer red corpuscles, but more colorless cor- 
puscles and more fibrin, than that in the splenic artery ; 
and it has been supposed that the spleen is one of those 
parts of the economy in which the colorless corpuscles of 
the blood are especially produced. 

157. The Gain of Heat— its Source. — It has been seen 
that heat is being constantly given off from the integument 
and from the air-passages ; and every thing that passes 
from the body carries away with it, in like manner, a cer- 
tain quantity of heat. Furthermore, the surface of the 
body is much more exposed to cold than its interior. 
Nevertheless, the temperature of the body is maintained 
very evenly, at all times and in all parts, within the range 
of two degrees on either side of 99° Fahr. 

This is the result of three conditions : The first, that 
heat is constantly being generated in the body ; the sec- 
ond, that it is as constantly being distributed through the 
body ; the third, that it is subject to incessant regulation. 

Heat is generated whenever oxidation takes place ;,and 
hence, whenever proteid substances (see 167) or fats, or 
amyloidal matters, are being converted into the more 
highly-oxidated waste products — urea, carbonic acid, and 
water — heat is necessarily evolved. But these processes 
are taking place in all parts of the body by which vital 
activity is manifested ; and hence every capillary vessel 



SOURCES OF GAIN To THE BLOOD. |5] 

and every extra-vascular islet of tissue is really a small tiro- 
plaoe in which heat is being evolved, in proportion to the 
activity of the chemical changes which are going en. 

158. Distribution of Heat by the Blood-Current— But, 
as the vital activities erf different parts of the body, and of 
the whole body, at different times, arc very different, and 

some parts o( the body are so >ituated as to lose their 
heat by radiation and conduction much more easily than 
others, the temperature of the body would he very unequal 
in its different parts, and at different times, were it not for 
the arrangements by which the heat is distributed and regu- 
lated. 

A\ hatever oxidation occurs in any part, raises the tem- 
perature nt the blood which is in that part at the time to 
a proportional extent. But this blood is swiftly hurried 
away into other regions o^ the body, and rapidlj gives up 
its increased temperature to them. On the other hand, 

the bleed which by being carried to the vessels in the >kin 
on the surface of the body begins to have 1 its temperature 
lowered by evaporation, etc., is hurried away, before it has 
time to get thoroughly cooled, into the deeper organs; and 
in them it becomes warm by contact, as well as by the 
oxidating processes in which it tafkes a part Thus the 
blood-vessels and their contents might be compared to a 
tern of hot-water pipes, through which the warm water 
is kept constantly circulating by a pump; while it is heated, 
not by a great central boiler as usual, but bya multitude of 
minute gas-jets, disposed beneath the pipes, not evenly, but 

more her.' and fewer there. It is obvious that, however 

much greater might be the heat applied to one part of the 
item of pipes than to another, the general temperature 

of the water would be even throughout, if it were kept 
moving with sufficient quickness by the pump. 

159. Evaporation regulates Temperature. — If such a 
item were entirely composed of closed pipes, the tem- 

• the water miLrht be raised to any extent by the 



152 ELEMENTARY PHYSIOLOGY. 

gas-jets. On the other hand, it might be kept down to 
any required degree by causing a larger, or smaller, por- 
tion of the pipes to be wetted with water, which should 
be able to evaporate freely — as, for example, by wrapping 
them in wet cloths. And the greater the quantity of 
water thus evaporated, the lower would be the tempera- 
ture of the whole apparatus. 

- Now, the regulation of the temperature of the human 
body is effected on this principle. The vessels are closed 
pipes, but a great number of them are inclosed in the 
skin and in the mucous membrane of the air-passages, 
which are, in a physical sense, wet cloths freely exposed to 
the air. It is the evaporation from these which exercises 
a more important influence than any other condition upon 
the regulation of the temperature of the blood, and, conse- 
quently, of the body. 

160. Regulative Agency of the Nervous System. — But, 
as a further nicety of adjustment, the wetness of the regu- 
lator is itself determined by the state of the small vessels, 
inasmuch as exudation from these takes place more readily 
when the walls of the veins and arteries are relaxed, and 
the blood distends them and the capillaries. But the con- 
dition of the walls of the vessels depends upon the nerves 
by which they are supplied ; and it so happens that cold 
affects these nerves in such a manner as to give rise to 
contraction of the small vessels, while moderate warmth 
has the reverse effect. 

Thus the supply of blood to the surface is lessened, and 
loss of heat is thereby checked, when the external tem- 
perature is low ; while, when the external temperature is 
high, the supply of blood to the surface is increased, the 
fluid exuded from the vessels pours out by the sweat- 
glands, and the evaporation of this fluid checks the rise in 
the temperature of the superficial blood. 

Hence it is that, so long as the surface of the body per- 
spires freely, and the air-passages are abundantly moist, a 



SOURCES OF GAIN TO THE BLOOD. i y; 

man may remain with impunity, for a considerable time, 
in an oven in which meat is being cooked. The heal of 
the air is expended in converting this superabundant per- 
spiration into vapor, and the temperature of the man's 

blood is hardly raised. 

161. Intermittent Action of the Glands. — The chief in- 
termittently activi sources of loss to the blood arc found 

among the glands proper, all of which are, in principle, 
narrow pouches of the mucous membranes, or of the in- 
tegument of the body, lined by a continuation of the epi- 
thelium, or of the epidermis. In the glands of TAeberkuhn, 
which exist in immense numbers in the walls of the small 
intestines, each gland is nothing more than a simple blind 
Bac of the mucous membrane, shaped like a small test-tube, 
with its closed end outwards, and its open end on the inner 
surface o( the intestine (Fig. 48, 1). The sweat-glands of 
the skin, as we have already seem, are equally simple, blind, 
tube-like involutions of the integument, the ends of which 
become coiled up. The sebaceous glands, usually connected 
with the hair-sacs, are shorter, and their blind ends are 
somewhat subdivided, so that the gland is divided into a 
narrow neck and a more dilated and sacculated end (Fig. 
48, 5). 

The neck by which the gland communicates with the 
free surface is called its duct. More complicated glands 
are produced by the elongation of the duct into a long 
tube, and the division and subdivision of the blind end 
into multitudes of similar tubes, each of which ends in a 
dilatation (Fig. 48, 6). These dilatations, attached to their 
branched ducts, somewhat resemble ;i bunch of isv.w 
Cilands of this kind arc called racemose. The salivary 
(/hinds and the pancreas are such glands. 

\ w\ many of tbsse glands, such n> the salivary, and 
tin- pancreas ( with tin* perspiratory, or sudoriparous glands, 
which it has been convenient to consider already), are only 
active when certain impressions on the nervous system 



154 



ELEMENTARY PHYSIOLOGY. 




Fig. 48. 
A Diagram to illustrate the Structure of Glands. 

A. Typical structure of the mucous membrane, a, an upper, and b. a lower, layer 
of epithelium cells; c, the dermis with e, a blood-vessel, and/, connective-tissue cor- 
puscles. 

B. The same, with only one layer of cells, a and b, the so-called basement mem- 
brane between the epithelium, a, and dermis, c. 

1. Simple tubular g-land. 

2. Tubular gland bind at its base. In this and Succeeding figures the blood- 
vessels are omitted. 

3. Simple saccular gland. 

4. Divided saccular gland, with a duct, d. 

5. Similar gland still more divided. 

C. Racemose gland, part only being drawn. 



SOURCES OF GAIN TO THE BLOOD. 155 

give rise to a particular condition of the gland, or of its 
vessels, or of both. 

162. Action of the Salivary Glands. — Thus the sight or 
smell, or even the thought of food, will cause a flow of 
saliva into the mouth ; the previously quiescent gland sud- 
denly pouring out its fluid secretion, as a result of a change 
in the condition of the nervous system. And, in animals, 
the salivary glands can be made to secrete abundantly, by 
irritating a nerve which supplies the gland and its vessels. 
How far this effect is the result of the mechanical influence 
of the nerve on the state of the circulation, by widening 
the small arteries (see 65) and so supplying the gland 
with more blood, and how far it is the result of a more 
direct influence of the nerve upon the state of the tissue 
o^l the gland itself, making the cells secrete, just as a nerve, 
when stimulated makes a muscle contract, is not at present 
finally determined. 

The liquids poured out by the intermittent glands are 
always very poor in solid constituents, and consist chiefly 
of water. Those poured on to the surface of the body are 
lost, but those which are received by the alimentary canal 
are doubtless in a great measure reabsorbed. 

163. Gain of Waste Products from the Muscles. — The 
great intermittent sources of gain of waste products to the 
blood are the muscles, every contraction of which is accom- 
panied by a pouring of certain products into the blood. 
That much of this waste is carbonic acid is certain from 
the facts (a) that the blood which leaves a contracting 
muscle is always highly venous, far more so than that 
which leaves a quiescent muscle; (6) that muscular exer- 
tion at once immensely increases the quantity of carbonic 

ftcid expired ; but whether the amount of nitrogenous 

waste is increased under these circumstances, or not, b a 

point yet under discussion. 



156 ELEMENTARY PHYSIOLOGY. 



CHAPTER VI. 

THE FUNCTION OF ALIMENTATION. 

Section I. — Properties of Food-Stuffs. 

164. The Alimentary Canal the Chief Source of Gain. 
— The great source of gain to the blood, and, except the 
lungs, the only channel by which altogether new material 
is introduced into that fluid, putting aside the altogether 
exceptional case of absorption by the skin, is the aliment- 
ary canal, the totality of the operations of which consti- 
tutes the function of alimentation. It will be useful to 
consider the general nature and results of the performance 
of this function before studying its details. 

165. Quantity of Dry, Solid, and Gaseous Aliment daily 
taken. — A man daily takes into his mouth, and thereby in- 
troduces into his alimentary canal, a certain quantity of solid 
and liquid food, in the shape of meat, bread, butter, water, 
and the like. The amount of chemically dry, solid matter, 
which must thus be taken into the body, if a man of 
average size and activity is neither to lose, nor to gain, in 
weight, has been found to be about 8,000 grains. In ad- 
dition to this, his blood absorbs by the lungs about 10,000 
grains of oxygen gas, making a grand total of 18,000 
grains (or nearly two pounds and three-quarters avoirdu- 
pois) of daily gain of dry, solid, and gaseous matter. 

166. Daily Loss of Dry Solids. — The weight of dry solid 
matter passed out from the alimentary canal does not, on 
the average, amount to more than one-tenth of that which 
is taken into it, or 800 grains. Now, the alimentary canal 
is the only channel by which any appreciable amount of 
solid matter leaves the body in an undissolved condition. 
It follows, therefore, that, in addition to the 10,000 grains 



PROPERTIES OF FOOD-STUFFS. 157 

of oxygen, 7,200 grains of dry, solid matter must pass out 
of the body by the lungs, skin, or kidneys, either in the 
form of gas, or dissolved in the liquid excretions of those 
organs. Further, as the general composition of the body 
remains constant, it follows either that the elementary con- 
stituents of the solids taken into the body must be identi- 
cal with those of the bod}' itself : or that, in the course of 
the vital processes, the food alone is destroyed, the sub- 
stance of the body remaining unchanged : or, finally, that 
both these alternatives hold good, and that food is, partly, 
identical with the wasting substance of the body, and re- 
places it ; and, partly, differs from the wasting substance, 
and is consumed without replacing it. 

167. Classification of Aliments. — As a matter of fact, all 
the substances which are used as food come under one of 
four heads. They are either what may be termed Pro- 
U ids, or they are Fats, or they are Amyloids, or they are 
Minerals. 

Proteids are composed of the four elements — carbon, 
hydrogen, oxygen, and nitrogen, sometimes united with 
sulphur and phosphorus. 

Under this head come the Gluten of flour ; the Albu- 
men of white of egg, and blood-serum; the Fibrin of the 
blood; the Syntonin, which is the chief constituent of 
muscle and flesh, and Casein, one of the chief constituents 
of cheese, and many other similar but less common bodies; 
while Gelatin, which is obtained, by boiling, from connec- 
tive tissue, and Chondrin, which may be produced in the 
same way from cartilage, may be considered to be outlying 
members of the same group. 

Fats are composed of carbon, hydrogen, and oxygon 
only, and contain more hydrogen than is enough to form 
water if united with the oxygen which they possess. 

All vegetable and animal fatly matters and oils come 
under this division. 

Amyloidswt substances which also consist of carbon, 



158 ELEMENTARY PHYSIOLOGY. 

hydrogen, and oxygen only. But they contain no more 
hydrogen than is just sufficient to produce water with 
their oxygen. These are the matters known as Starch, 
Dextrine, Sugar, and Gum. 

It is the peculiarity of the three groups of food-stuffs 
just mentioned that they can only be obtained (at any 
rate, at present) by the activity of living beings, whether 
animals or plants, so that they may be conveniently termed 
v ital food-stuffs. 

Food-stuffs of the fourth class, on the other hand, or 
Minerals, are to be procured as well from the not-living, 
as the living world. They are water, and salts of sundry 
alkalies, earths, and metals. To these, in strictness, oxy- 
gen ought to be added, though, as it is not taken in by the 
alimentary canal, it hardly comes within the ordinary ac- 
ceptation of the word food. 

168. Ultimate Composition of Aliments. — In ultimate 
analysis, then, it appears that vital food -stuffs contain 
either three or four of the elements : carbon, hydrogen, 
oxygen, and nitrogen; and that mineral food -stuffs are 
water and salts. But the human body, in ultimate analy- 
sis, also proves to be composed of the same four elements, 
plus water, and the same saline matters as are found in 
food. 

More than this, no substance can serve permanently for 
food — that is to say, can prevent loss of weight and change 
in the general composition of the body — unless it contains a 
certain amount of proteid matter in the shape of albumen, 
fibrin, syntonin, casein, etc. ; while, on the other hand, any 
substance which contains proteid matter, in a readily as- 
similable shape, is competent to act as a permanent vital 
food-stuff. 

The human body, as we have seen, contains a large 
quantity of proteid matter in one or other of the forms 
which have been enumerated ; and, therefore, it turns out 
to be an indispensable condition that every substance, 



PROPERTIES OF FOOD-STUFFS. 159 

which is to serve permanently as food, must contain a suf- 
ficient quantity of the most important and complex com- 
ponent o( the body ready made. It must also contain a 
sufficient quantity o( the mineral ingredients which are re- 
quired. Whether it contains either fats or amyloids, or 
both, its essentia] power of supporting the life and main- 
taining the weight and composition of the body remains 
unchanged. 

169. No Absolute Necessity for Other Food-Stuffs.— The 
necessity of constantly renewing the supply of proteid 
matter arises from the circumstance that the secretion of 
urea from the body (and consequently the loss of nitrogen) 

s on continually, whether the body is fed or not : while 
there is only one form in which nitrogen (at any rate, in 
any considerable quantity) can be taken into the blood, 
and that is in the form of a solution of proteid matter. If 
proteid matter be not supplied, therefore, the body must 
needs waste, because there is nothing in the food com- 
petent to make good the loss of nitrogen. 

On the other hand, if proteid matter be supplied, there 
can be no absolute necessity for any other but the mineral 
food- stuffs, because proteid matter contains carbon and 
hydrogen in abundance, and hence is competent to give 
origin to the other great products of waste, carbonic acid 
and water. 

In fact, the final results of the oxidation of proteid 
matters are carbonic acid, water, and ammonia; and these, 
IS we have seen, are the final shapes of the waste products 
of the human economy. 

170. Nitrogen Starvation. — From what has been said, 
it becomes readily intelligible that, whether an animal be 
herbivorous or carnivorous, it begins to starve from the 

moment its vital food-st lift's consist of pure amyloids, or 

any mixture of them. It Buffers from what may be 
called nitrogen starvation, and, sooner or later, will die. 

In this case, and still more in thai of an animal de- 



160 ELEMENTARY PHYSIOLOGY. 

prived of vital food altogether, the organism, so long as it 
continues to live, feeds upon itself. In the former case, 
those excretions which contain nitrogen, in the latter, all 
its waste products, are necessarily formed at the expense 
of its own body ; w4ience it has been rightly enough ob- 
served that a starving sheep is as much a carnivore as a 
lion. 

171. Disadvantages of a Purely Nitrogenous Diet— But 
though proteid matter is the essential element of food, and 
under certain circumstances may suffice, by itself, to main- 
tain the body, it is a very disadvantageous and uneconom- 
ical food. 

Albumen, which may be taken as the type of the pro- 
teids, contains about 53 parts of carbon and 15 of nitrogen 
in 100 parts. If a man were to be fed on white of egg^ 
therefore, he would take in, speaking roughty, 3^ parts of 
carbon for every part of nitrogen. 

But it is proved experimentally, that a healthy, full- 
grown man, keeping up his weight and heat, and taking a 
fair amount of exercise, eliminates 4,000 grains of carbon 
to only 300 grains of nitrogen, or, roughly, only needs one- 
thirteenth as much nitrogen as carbon. However, if he is 
to get his 4,000 grains of carbon out of albumen, he must 
eat 7,547 grains of that substance. But 7,547 grains of 
albumen contain 1,132 grains of nitrogen, or nearly four 
times as much as he wants. 

To put the case in another way, it takes about four 
pounds of fatless meat (which generally contains about 
one-fourth its weight of dry solid proteid s) to yield 4,000 
grains of carbon, whereas one pound will furnish 300 
grains of nitrogen. 

Thus a man, confined to a purely proteid diet, must eat 
a prodigious quantity of it. This not only involves a great 
amount of physiological labor in comminuting the food, 
and a great expenditure of power and time in dissolving 
and absorbing it, but throws a great quantity of wholly 



PROPERTIES OF FOOD-STUFFS. 101 

profitless labor upon those excretory organs, winch have 
to get rid of the nitrogenous matter, three-fourths of which, 

a> we have seen, is superfluous. 

172. Economy of Physiological Power. — Unproductive 
labor is as much to be avoided in physiological, as in 
political, economy : and it is quite possible 4 that an animal 
fed with perfectly nutritious, proteid matter should die of 

rvation: the loss of power in various operations re- 
quired tor its assimilation overbalancing the gain; or the 
time occupied iti their performance being too great to 
check waste with sufficient rapidity. The body, under 
these circumstances, falls into the condition of a merchant 
who has abundant assets, but who cannot get in his debts 
in time to meet his creditors. 

173. Economy of a Mixed Diet. — These considerations 
lead us to the physiological justification of the universal 
practice of mankind in adopting a mixed diet, in which 
proteids are mixed either with fats, or with amyloids, or 
with both. 

Fats may be taken to contain about 80 per cent, of 
carbon, and amyloids about 40 per cent. Now, it has been 

i that there is enough nitrogen to supply the waste of 
that substance per diem, in a healthy man, in a pound of 
tatless moat ; which also contains 1,000 grains of carbon, 
leaving a deficit of 3,000 grains of carbon. Rather more 

ii halt* a pound of fat, or a pound of sugar, will supply 
- quantity of carbon. The former, if properly subdi- 
vided, the bitter, by reason of its solubility, passes with 
into the economy, the digestive labor of which 
i- consequently reduced to a minimum. 

174. Advantages of a Mixed Diet. — Several apparently 
simple articles of food constitute ;t mixed diet in them- 

Thus butcher's meal commonly contains from 30 to 
50 per rent, of fit. Bread, on the other hand, contains the 
proteid, gluten, and th<- amyloids, starch and sugar, with 

minute quantities of fat. Hut. from the proportion in 

11 



162 ELEMENTARY PHYSIOLOGY. 

which these proteid and other constituents exist in these 
substances, they are neither, taken alone, such physiologi- 
cally economical foods as they are when combined in the 
proportion of about 200 to 75 ; or two pounds of bread to 
three-quarters of a pound of meat per diem. 

175. Intermediate Changes of the Food. — It is quite 
certain that nine-tenths of the dry, solid food which is 
taken into the body sooner or later leaves it in the shape 
of carbonic acid, w^ater, and urea (or uric acid) ; and it is 
also certain that the compounds which leave the body not 
only are more highly oxidized than those which enter it, 
but in them is carried away out of the body all the oxygen 
taken into the blood by the lungs. 

The intermediate stages of this conversion are, how- 
ever, by no means so clear. It is highly probable that the 
amyloids and fats are very frequently oxidized in the blood, 
without, properly speaking, ever forming an integral part 
of the substance of the body ; but whether the proteids 
may undergo the same changes in the blood, or whether it 
is necessary for them first to be incorporated with the 
living tissue, is not positively known. 

So, again, it is certain that, in becoming oxidized, the 
elements of the food must give off heat, and it is probable 
that this heat is sufficient to account for all that is given 
off by the body ; but it is possible, and indeed probable, 
that there may be other minor sources of heat. 

176. Objections to the Common Classification. — Food- 
stuffs have been divided into heat-producers and tissue- 
formers — the amyloids and fats constituting the former 
division, the proteids the latter. But this is a very mis- 
leading classification, inasmuch as it implies, on the one 
hand, that the oxidation of the proteids does not develop 
heat ; and, on the other, that the amyloids and fats, as 
they oxidize, subserve only the production of heat. 

Proteids are tissue-formers, inasmuch as no tissue can 
be produced without them ; but they are also heat-pro- 



PRELIMINARIES OF DIGESTION. 163 

ducer&i not only directly, but because, as we have seen 
53, 154), they are competent to give pise to amyloids 
by chemical metamorphosis within the body. 

If it is worth while to make a special classification of 

the vital food-stuffs at all, it appears desirable to distin- 
guish the essential food-stufis, or proteids, from the ae 

/ food-stuffs, or fats and amyloids — the former alone 
being, in the nature of things, necessary to life, while the 
latter, however important, are not absolutely necessary. 

177. Purpose of the Alimentary Mechanism. — All food- 
stuffs being thus proteids, fats, amyloids, or mineral mat- 

s, pure or mixed up with other substances, the whole 
purpose of the alimentary apparatus is to separate these 
proteids, etc., from the innutritions residue, if there be any; 
and to reduce them into a condition either of solution 
or of excessively fine subdivision, in order that they may 
make their way through the delicate structures which form 
the walls of the yessels of the alimentary canal. To these 

Is food is taken into the mouth and masticated, is mixed 
with saliva, is swallowed, undergoes gastric digestion, 
passes into the intestine, and is subjected to the action of 
the secretions of the glands attached to that viscus ; and, 
finally, after the more or less complete extraction of the 
nutritive constituents, the residue, mixed up with certain 
secretions of the intestines, leaves the bod}' as the fceces. 

>r.« tiox TT. — Preliminaries of Digestion* 

178. The Month and Pharynx. — The cavity of the 
mouth is a chamber with a fixed roof, formed by the hard 
palaU (Fig. 49, I), and with a movable tl'xT. constituted 
by the lower jaw, and the tongue (/•'). which fills up the 

between the two branches of the jaw. Arching 
round the margins of the upper and the lower jaws an* the 
thirty-two teeth, sixteen above and sixteen below, and exter- 
nal to these, the closure of the cavity of the mouth is com- 
pleted by the cheeks a1 the -ides, and by the lips in front 



164 



ELEMENTARY PHYSIOLOGY. 



When the mouth is shut, the back of the tongue comes 
into close contact with the palate ; and, where the hard 
palate ends, the communication between the mouth and 
the back of the throat is still further impeded by a sort of 
fleshy curtain — the soft palate or velum — the middle -of 
which is produced into a prolongation, the uvula (/), 
while its sides, skirting the sides of the passage, or fauces , 
form double muscular pillars, which are termed the pillars 
of the fauces. Between these the tonsils are situated, one 
on each side. 




TV 



Fig. 49. 

A Section of the Mouth and Nose taken vertically, a little to the left of 
the Middle Line. 

a, the vertebral column; ft, the gullet; c, the windpipe; d, the thyroid cartilage 
of the larynx; e, the epiglottis; f\ the uvula; g, the opening- of the left Eustachian 
tube ; 7i, the opening of the left lachrymal duct ; i, the hyoid bone ; k, the tongue ; I, 
the hard palate ; m, n, the base of the skull ; o, p. q, the superior, middle, and inferior 
turbinal bones. The letters g,f, e, are placed in the pharynx. 






PRELIMINARIES OF DIGESTION. 105 

The velum with its uvula comes into contact below 
with the upper part oi' the back of the tongue, and with a 
sort of gristly , lid-like process connected with its base, the 
epiglottis (<). 

Behind the partition thus formed lies the cavity of the 
pharynx^ which may be described as a funnel-shaped bag 
with muscular walls, the upper margins of the Blanting, 
wide end of which are attached to the base of the skull, 
while the lateral margins are continuous with the sides, 
and the lower with the floor, of the mouth. The narrow 
end of the pharyngeal bag passes into the gullet or 

tphagus (#), a muscular tube, which affords a passage 
into the stomach. 

There are no fewer than six distinct openings into the 
front part of the pharynx — four in pairs, and two single 
ones in the middle line. The two pairs are, in front, the 
hinder openings of the nasal cavities ; and at the sides, 
(lose to these, the apertures of the Eustachian tubes (g). 
The two single apertures are, the hinder opening of the 
mouth between the soft palate and the epiglottis ; and, 
behind the epiglottis, the upper aperture of the respiratory 
passage, or the glottis. 

179. The Salivary Glands. — The mucous membrane 
which lines the mouth and the pharynx is beset with 
minute glands, the buccal glands ; but the great glands 
from which the cavity of the mouth receives its chief se- 
cretion are the three pairs which, as has been already men- 
tioned, are called parotid, submaxillary, sublingual, and 
which secrete the principal part of the 1 saliva (Fig. 50). 

Each parotid gland is placed just in front of the ear, 

and its duct passes forwards along the check, until it opens 
in the interior of the mouth, opposite the second upper 
grinding tooth. 

The submaxillary and sublingual glands lie between the 

lower jaw and the floor of the mouth, the submaxillary 
being Bituated farther baek than the sublingual. Their 



166 ELEMENTARY PHYSIOLOGY. 

ducts open in the floor of the mouth below the tip of the 
tongue. The secretion of these salivary glands, mixed 
with that of the small glands of the mouth, constitutes the 
saliva — a fluid which, though thin and watery, contains a 
small quantity of animal matter, called Ptyalin, which has 
certain very peculiar properties. It does not act upon pro- 
teid food-stuffs, nor upon fats ; but, if mixed with starch, 
and kept at a moderate warm temperature, it turns that 
starch into grape-sugar. The importance of this operation 




Fig. 50. 

A dissection of the right side of the face, showing a, the sublingual ; 5, the sub- 
maxillary glands, with their ducts opening beside the tongue in the floor of the mouth 
at d; c, the parotid gland and its duct, which opens on the side of the cheek at e. 

becomes apparent when one reflects that starch is insol- 
uble, and therefore, as such, useless as nutriment, while 
sugar is highly soluble, and readily oxidizable. 

180. The Teeth.— Each of the thirty-two teeth which 
have been mentioned consists of a crown which projects 
above the gum, and of one or more fangs, which are em- 
bedded in sockets, or what are called alveoli, in the jaws. 

The eight teeth on opposite sides of the same jaw are 
constructed upon exactly similar patterns, while the eight 
teeth, which are opposite to one another, and bite against 
one another above and below, though similar in kind, differ 
somewhat in the details of their patterns. 



PRELIMINARY OF DIGESTION. 107 

The two tooth in each eight which are nearest the mid- 
dle line in the front of the jaw, have wide but sharp and 
chisel-like edges. Hence they art 4 called incisors, or cut- 
ting teeth. The tooth which comes next is a tooth with a 
more conical and pointed crown. It answers to the great 
tearing and holding tooth of the dog, and is called the 
or eye-tooth. The next two teeth have broader 
crowns, with two cusps, or points, on eaeli crown, one on 
the inside and one on tin 4 outside, whence they are termed 
uspid teeth, and sometimes false grinders. All these 
teeth have usually one fang each, except the bicuspid, the 
fangs o{ which may be more or less completely divided into 
two. The remaining teeth have two or three fangs each, 
and their crowns are much broader. As they crush and 
grind the matters which pass between them, they are called 
molars, or true grinders. In the upper jaw their crowns 
present four points at the four corners, and a diagonal ridge 
connecting two of them. In the lower jaw the complete 
pattern is rive-pointed, there being two cusps on the inner 
side and three on the outer. 

181. Working of the Jaw. — The muscles of the parts 
which have been described have such a disposition that the 
lower jaw can be depressed, so as to open the mouth and 

irate the teeth ; or raised, in such a manner as to bring 
the teeth together; or move obliquely from side to side, so 
a- to cause the face of the grinding teeth and the edges of 
the cutting teeth to slide over one another. And the muscles 
which perform the elevating and sliding movements are of 
strength, and confer a corresponding force upon the 
grinding and cutting actions of the teeth. In correspond- 
ence with the pressure they have to resist, the superficial 
substance of the crown of the teeth is of greal hardness, 
ing formed of enamel, which i^ the hardesl substance 

in the body, SO dense and hard, indeed, thai it will strike 
♦ire with steel («& 352). But. notwithstanding its ex- 
treme hardness, it becomes worn down in old persons, 



1G8 ELEMENTARY PHYSIOLOGY. 

and, at an earlier age, in savages who live on coarse 
food. 

182. Masticating and Swallowing. — When solid food is 
taken into the mouth, it is cut and ground by the teeth, 
the fragments which ooze out upon the outer side of their 
crowns being pushed beneath them again by the muscular 
contractions of the cheeks and lips; while those which 
escape on the inner side are thrust back by the tongue, 
until the whole is thoroughly rubbed down. 

While mastication is proceeding, the salivary glands 
pour out their secretion in great abundance, and the saliva 
mixes with the food, which thus becomes interpenetrated 
not only with the salivary fluid, but with the air which is 
entangled in the bubbles of the saliva. 

When the food is sufficiently ground it is collected, en- 
veloped in saliva, into a mass or bolus, which rests upon 
the back of the tongue, and is carried backwards to the 
aperture which leads into the pharynx. Through this it 
is thrust, the soft palate being lifted and its pillars being 
brought together, while the backward movement of the 
tongue at once propels the mass and causes the epiglottis 
to incline backwards and downwards over the glottis, and 
so to form a bridge by which the bolus can travel over the 
opening of the air-passage without any risk of tumbling 
into it. While the epiglottis directs the course of the 
mass of food below, and prevents it from passing into the 
trachea, the soft palate guides it above, keeps it out of the 
nasal chamber, and directs it downwards and backwards 
towards the lower part of the muscular pharyngeal funnel. 
By this the bolus is immediately seized and tightly held, 
and the muscular fibres contracting above it, while they are 
comparatively lax below, it is rapidly thrust into the oesoph- 
agus. By the muscular walls of this tube it is grasped 
and propelled onwards, in a similar fashion, until it reaches 
the stomach. 

183. Drinking, — Drink is taken in exactly the same way. 



STOMACH-DIGESTION. 109 

It does not fall down the pharynx and gullet, but each gulp 
is grasped and passed down. Hence it is that jugglers are 
able to drink standing upon their heads, and that a horse, 
or ox, drinks with its throat lower than its stomach, feats 
which would be impossible if fluid simply fell down the 
gullet into the gastric cavity. 

During these processes of mastication, insalivation, and 
deglutition, what happens to the food is, first, that it is 
1 educed to a coarser or finer pulp; secondly, that any mat- 
ters it carries in solution are still more diluted by the water 
of the saliva ; thirdly, thai any starch it may contain begins 
to be changed into sugar by the peculiar constituent (ptya- 
lin) of the saliva. 

Section III. — Stomach-Digestion. 

184. The Stomach and the Gastric Juice. — The stomach, 
like the gullet, consists of a tube with muscular walls com- 
posed of smooth muscular fibres, and lined by an epithe- 
lium ; but it differs from the gullet in several circumstances. 
In the first place, its cavity is greatly larger, and its left 
end is produced into an enlargement which, because it is 
on the heart-side of the body, is called the cardiac dilata- 
tion (Fig. 51, h). The opening of the gullet into the stom- 
ach, termed the cardiac aperture, is consequently nearly 
in the middle of the whole length of the organ, which pre- 
sents a long, convex, greater curvature, along its front or 
under edge, and a short concave, lesser curvature, on its* 
back or upper contour. Towards its right extremity the 

nach narrows, and, where it passes into the intestine, 
the muscular fibres are so disposed as to form a sort ol 
sphincter around the aperture ol" communication. This is 
called the pylorus (Fig, 51, d). 

The mucous membrane lining the wall of the stomach 

i- very delicate, and multitudes of small glands open upon 

it- surface. Some of these arc Bimple, but others (Fig. 52) 
t somewhai more complicated structure, their blind 



170 



ELEMENTARY PHYSIOLOGY. 



ends being subdivided. It is these glands, and more es- 
pecially the more complicated ones, the so-called peptic 
glands, which, when food passes into the stomach, throw 
out a thin acid fluid, the gastric juice. 

When the stomach is empty, its mucous membrane is 
pale and hardly more than moist. Its small arteries are 
then in a state of contraction, and comparatively little 
blood is sent through it. On the entrance of food, a ner- 
vous action is set up, which causes these small arteries to 
dilate ; the mucous membrane consequently receives a 
much larger quantity of blood, it becomes very red, little 




The Stomach laid open behind. 

a, the cesophag-us ; b, the cardiac dilatation ; c, the lesser curvature ; d, the pylorus ; 
e, the biliary duct; /, the gall-bladder; g* the pancreatic duct, opening- in common with 
the cystic duct opposite h; h, i, the duodenum. 



drops of fluid gather at the mouth of the glands, and finally 
run down as gastric juice. The process is very similar to 
the combined blushing and sweating which takes place 
when the sympathetic in the neck is divided. 

Pure gastric juice appears to consist of little more than 
water, containing a few saline matters in solution, and its 



STOMACH-DIGESTION, 1 7 1 

acidity is due to the presence of free hydrochloric acid; it 
sses, however, in addition a small quantity of a pecu- 
liar substance railed pepsin, which seems to be not alto- 
gether dissimilar in chemical composition to, though very 
different in its effects trom^ptyalin (179). 

Thus, when the food passes into the stomach, the con- 
tractions of that organ roll it alxmt and mix it thoroughly 
with the gastric juice. 

185. Artificial Digestion. — It is easy to ascertain the 
properties of gastric juice experimentally, by putting a 
small portion of that part of the mucous membrane which 
contains the peptic glands into acidulated water containing 
small pieces of meat, hard-boiled egg, or other proteids, 
and keeping the mixture at a temperature of about 100°. 
After a few hours it will be found that the white of egg, 
if not in too great quantity, has become dissolved ; while 
all that remains of the meat is a pulp, consisting chiefly of 
the connective tissue and fatty matters which it contained. 
This is artificial digestion, and it has been proved by ex- 
periment that precisely the same operation takes place 
when food undergoes natural digestion within the stomach 
of a living animal. 

The proteid solution thus effected is called a pteptone, 
and has pretty much the same characters, whatever the 
nature of the proteid which has been digested. 

186. Osmosis. — Peptone differs from all other proteids 
in its extreme solubility, and in the readiness with which 
it parses through animal membranes. Many proteids, as 
fibrin, arc naturally insoluble in water, and others, such as 

white of cM-g, though apparently soluble, are not completely 

. and can be rendered quite solid or coagulated by being 
Bimply heated, as when an egg is boiled. A solution of 
peptone, however, is perfectly fluid, does not become solid, 

and t- not at all coagulated by boiling. Again, if a quan- 
tity of whit.- of egg be tied up in a bladder, and the blad- 
Unmersed in water, very little of the proteid will pa-- 



172 



ELEMENTARY PHYSIOLOGY. 



through the bladder into the water, provided that there are 
no holes. If, however, peptone be used instead of albumen, 
a very large quantity will speedily pass through into the 
water, and a quantity of water will pass from the outside 
into the bladder, causing it to swell up. This process is 
called osmosis, and is evidently of great importance in the 
economy ; and the purpose of the conversion of the various 
proteids by digestion into peptone seems to be, in part at 




Fig. 52. 

One of the Glands, which secrete the Gastric Juice, magnified about three hundred and 

fifty diameters. 

least, to enable this class of food-stuff to pass readily into 
the blood through the thin partition formed by the walls 
of the mucous membrane of the intestine and the coats of 
the capillaries. 

Similarly, starch, even when boiled, and so partially 



STOMAOH-DNiESTIOX. 



173 



dissolved, will not pass through membranes, whereas sugar 
does so with the greatest ease. Ilenee the reason of the 




Fie. 68. 

Thf. v v ri\nr.iT lb bbbs rpoB -imply orarnra tut Catitdm of tub 

m« AbUOMVM witiioit wv rtTKHEB DlSSKOTION. 

: A. diaphragm ; i '. ventricles 

of th' - ,i. and oo- 

ir ii in- mbrani - ; /. cartilage 

at t of Th«- wall of tin- l"><ly I. ft 

*; /.. th<- liver. In this ease lying 
ft than the right of 1 irt of the greater 

■ ' : /' B( nil. BO Lai - 

develop Q th< 1 1-_-' int. 



174 ELEMENTARY PHYSIOLOGY. 

conversion of starch, by digestion, into sugar. It takes a 
very long time (some days) for the dilute acid alone to 
dissolve proteid matters, and hence the solvent power of 
gastric juice must be chiefly attributed to the pepsin. 

As far as we know, gastric juice has no direct action on 
fats ; by breaking up, however, the proteid framework in 
which animal and vegetable fats are embedded, it sets these 
free, arid so helps their digestion by exposing them to the 
action of other agents. It appears, too, that gastric juice 
has no direct action on amyloids ; on the contrary, the con- 
version of the starch into sugar, begun in the mouth, appears 
to be wholly or partially arrested by the acidity of the con- 
tents of the stomach, ptyalin being active only in an alka- 
line or neutral mixture. 

187. Absorption from the Stomach. — By continual roll- 
ing about, with constant additions of gastric juice, the food 
becomes reduced to the consistence of pea-soup, and is 
called chyme. In this state it is, in part, allowed to escape 
through the pylorus and to enter the duodenum ; but a 
great deal of the fluid (consisting of peptone, together with 
any saccharine fluids resulting from the partial conversion 
of starch, or otherwise), is at once absorbed, making its 
way, by imbibition, through the walls of the delicate and 
numerous vessels of the stomach into the current of the 
blood, which is rushing through the gastric veins to the 
vena portm. 

Section IV. — Intestinal Digestion. 

188. The Large and Small Intestines. — The intestines 
form one long tube, with mucous and muscular coats, like 
the stomach ; and, like it, they are enveloped in perito- 
neum. They are divided into two portions — the small in- 
testines and the large intestines ; the latter having a much 
greater diameter than the former. The small intestines 
again are subdivided into the duodenum, the jejunum, and 
the ileum, but there is no natural line of demarcation be- 



INTESTINAL DIGESTION. 175 

tween these. The duodenum, however, is distinguishable 
as that part of the small intestine which immediately suc- 
ceeds the stomach, and is bent upon itself and fastened by 
the peritoneum against the back wall of the abdomen, in 
the loop shown in Fig. 51. It is in this loop that the head 
of tin 1 pancreas lies (Fig. 47). 

The ileum (Fig. 5-4, a), is no wider than the jejunum or 
duodenum, so that the transition from the small intestine 
to the large (e) is quite sudden. The opening of the small 
intestine into the large is provided with prominent lips 




Fig. 54. 

The termination of the- ileum, a. in the cecum, and the continuation of the latter 
Into the colon, e : 'L the ileocecal valve : e. the aperture of the appendix revmifor- 
into the ca?cum. 

which project into the cavity of the latter, and oppose the 
passage of matters from it into the small intestine, while 
they readily allow of a passage the other way. This is the 
Ueo-ccecal valve (Fig. 54, d). 

The large intestine forms a blind dilatation beyond the 
ileo-r-npeal valve, which is called the CCBCUm ; and from 
this an elongated, blind proce89 is given off, which, from 

it- shape, is called the vermiform appendix of the caecum 
(Pig. 54, b). 

The caecum lies in the lower pait of the light side of 
the abdominal cavity. The eofcm, or first part of the larrre 



176 



ELEMENTARY PHYSIOLOGY. 



intestine, passes upwards from it as the ascending colon y 
then making a sudden turn at a right angle, it passes across 
to the left side of the body, being called the transverse 
colon in this part of its course ; and next, suddenly bend- 
ing backwards along the left side of the abdomen, it be- 




Fig. 55. 

Semi-diagrammatic View of Two Villi of the Small Intestines. 
(Magnified about fifty diameters.) 

«, substance of the villus ; b, its epithelium, of which some cells are seen detached 
at b 1 ; c, 6?, the artery and vein, with their connecting- capillary net-work, which en- 
velops and hides <?, the lacteal radicle which occupies the centre of the villus and 
opens into a net- work of lacteal vessels at its base. 

comes the descending colon. This reaches the middle line 
and becomes the rectum, which is that part of the large 
intestine which opens externally. 

189. Their Parts and Actions. — The mucous membrane 
of the whole intestine is provided with numerous small and 
simple glands (named after Lieberklihn), which pour into 
it a secretion, the intestinal juice, the precise functions of 
which are unknown, though it appears in some creatures 
at least to possess the power of converting starch into 
sugar, and proteids into peptone. At the commencement 
of the duodenum are certain racemose glands, called the 
glands of Brunner, whose function is wholly unknown. 

Structures peculiar to the small intestine are the val- 
vules conniventes, transverse folds of the mucous mem- 
brane, which increase the surface ; and the villi, which are 



INTESTINAL DIGESTION. 177 

minute thread-like processes of the mucous membrane on 
the valvules conniventes and elsewhere, set side by side, 
like the pile o( velvet. Each villus is coated by epithe- 
lium, and contains in its interior the radicle, or commence- 
ment, of a lacteal vessel (44), between which and the epi- 
thelium lies a capillary net-work with its afferent artery 
and efferent vein. The intestines receive their blood almost 
directly from the aorta. Their veins carry the blood which 
has traversed the intestinal capillaries to the venaportCB. 

190. Peristaltic Contraction. — The fibres of the mus- 
cular coat of the intestines (which lies between the mucous 
membrane and the serous, or peritoneal, investment) are 
disposed longitudinally and circularly ; the longitudinal 
coat being much thinner, and placed outside the circular 
coat. Now, the circular fibres of any part contract, suc- 
cessively, in such a manner that the lower fibres, or those 
on the side of the anus, contract after the upper ones, or 
those on the side of the pylorus. It follows from this 
so-called peristaltic contraction, that the contents of the 
intestines are constantly being propelled, by successive 
and progressive narrowing of their calibre, from their 
upper towards their lower parts. 

The large intestine presents noteworthy peculiarities in 
the arrangement of the longitudinal muscular fibres of the 
colon into three bands, which are shorter than the walls 
of the intestine itself, so that the latter is thrown into 
puckers and pouches; and in the disposition of muscular 
fibres around the termination of the rectum into a ring-like 
sphincter muscle, which keeps the aperture firmly closed, 
!»t when defecation takes place. 

191. Entrance of Bile and Pancreatic Juice. — The only 
retions, besides those of the proper intestinal glands, 

which enter the intestine, are those of the liver and the 
pancreas — the bile and the pancreatic juice. The ducts of 
these organs have a common opening in the middle of the 
bend of the duodenum ; and, -in ••■ the common duct passes 



IT 8 ELEMENTARY PHYSIOLOGY. 

obliquely through the coats of the intestine, its walls serve 
as a kind of valve, obstructing the flow of the contents of 
the duodenum into the duct, but readily permitting the 
passage of bile and pancreatic juice into the duodenum 
(Figs. 44, 47, 51). 

Pancreatic juice is an alkaline fluid not unlike saliva in 
many respects ; it differs, however, in containing a consid- 
erable quantity of proteid material. Bile we have already 
studied. 

After gastric digestion has been going on some time, 
and the semi - digested food begins to pass on into the 
duodenum, the pancreas comes into activity, its blood-ves- 
sels dilate, it becomes red and full of blood, its cells secrete 
rapidly, and a copious flow of pancreatic juice takes place 
along its duct into the intestine. 

The secretion of bile by the liver is much more con- 
tinuous than that of the pancreas, and is not so markedly 
increased by the presence of food in the stomach. There 
is, however, a store of bile laid up in the gall-bladder; and 
as the acid chyme passes into the duodenum, and flows 
over the common aperture of the gall and pancreatic ducts, 
a quantity of bile from this reservoir in the gall-bladder is 
ejected into the intestine. The bile and pancreatic juice 
together here mix with the chyme and convert it into what 
is called chyle, 

192. Chyle— Absorption from the Intestines. — Chyle dif- 
fers from chyme in two respects. In the first place, the 
alkali of the bile neutralizes the acid of the chyme ; in the 
second place, both the bile and the pancreatic juice appear 
to exercise an influence over the fatty matters contained in 
the chyme, which facilitates the subdivision of these fats 
into very minute separate particles. The chyme, in fact, 
which results from the digestion of fatty food, is a mere 
mixture of w^atery fluid with oily matters, which are ready 
to separate from it and unite with one another. In the 
chyle, on the other hand, the fatty matters are suspended 



INTESTINAL DIGESTION. 179 

in the fluid, just as oil may be evenly diffused through 
water by gradually rubbing it up with white of egg into 
what is termed an emulsion ; or as the fat (that is, the 

butter) of milk is naturally held suspended in the watery 
- of milk. 

The chyle, with these suspended particles, looks white 
and milky, for the same reason that milk has the same 
aspect — the multitude of minute suspended fatty particles 
reflecting a great amount of light. 

The conversion of starch into sugar, which seems to be 
spended wholly, or partially, so long as the food remains 
in the storaaoh, on account of the acidity of the chyme, is 
resumed as soon as the latter is neutralized, the pancreatic 
and intestinal juices operating powerfully in this direction. 
Recent observations, moreover, have shown that pan- 
it ic juice has a powerful effect on proteid matters, con- 
verting them into peptones differing little, if at all, from 
the peptones resulting from gastric digestion. It would 
appear, too, that fats are not only minutely divided or 
emulsionized by the bile and pancreatic juice, i. e., acted 
upon mechanically, but also to a small extent converted by 
a chemical change into soaps, and thus rendered more solu- 
ble. Hence it appears that, while in the mouth amyloids 
only, and in the stomach proteids only, are digested, in 
the intestine all three kinds of food-stuffs, proteids, fats, 
and amyloids, are either completely dissolved or minutely 
subdivided, and so prepared for their passage into the 
sels. 

Aa the chyle is thrust along the small intestines by the 

• ion of the peristaltic contractions, the dissolved 

matter which it contain- is absorbed, in the ordinary way, 

by osm< sia into the vessels of the villi. The minute par- 
ticles of fatty matter, on the other hand, which, not being 
dissolved, are incapable of osmosis, pass bodily through 
the soft substance of the epithelium into that of the villi, 
and ><» into the beginning of tin* lacteal, 



180 ELEMENTARY PHYSIOLOGY. 

The exact manner in which this is effected is at present 
a matter of dispute. The contents of the intestine are un- 
doubtedly subject to pressure from the peristaltic contrac- 
tions of the muscular walls ; and this may help to squeeze 
the fat into the villi, just as mercury may be squeezed 
through the pores of a piece of wash-leather. The pro- 
cess, however, is probably not one of mere pressure only. 

As the net-work of capillaries lies outside the lacteal 
radicle in each villus, it would appear probable that the 
blood-vessels must carry off the greater part of the more 
soluble matters of the chyle. It is possible, however, that 
some of these pass by simple diffusion into the lacteals as 
well as into the blood-vessels. We are not, in fact, in pos- 
session of exact knowledge as to which constituents of the 
chyle pass into the lacteals, and which into the blood-ves- 
sels (or which into both), except on one point ; and that is, 
that the minutely-divided fat passes not into the blood- 
vessels, but into the lacteals, fills them, and only enters 
the blood after a roundabout passage through the mesen- 
teric lymphatics and the thoracic duct (43, 44). 

193. Digestion in the Large Intestines. — The digested 
matters, as they are driven along the small intestines, 
gradually become deprived of their peptones, fats, and 
soluble amyloids, and are forced through the ileo-caecal 
valve into the caecum and large intestine. Here they 
acquire an acid reaction and the characteristic fecal odor 
and color, which become more and more marked as they 
approach the rectum. It has been supposed that a sort 
of second digestion occurs in the upper part of the large 
intestine. 



INSTRUMENTS OF MOTION 181 



CHAPTER VII. 
MoTIv >" axi> LOCOMOTION. 

Section I. — Instrument* of Motion. 

194. The Vital Eddy.— In the preceding chapters the 
manner in which the incomings of the human body are 

averted into its outgoings has been explained. It has 
been seen that new matter, in the form oi vital and min- 
eral foods, is constantly appropriated by the body, to 
make up for the loss oi old matter, in the shape, chiefly, 
of carbonic acid, urea, and water, which is as constantly 

:ig on. 

The vital foods are derived directly, or indirectly, from 
the vegetable world : and the products of waste either are 
such compounds as abound in the mineral world, or im- 
mediately decompose into them. Consequently, the human 
body is the centre of a stream of matter which sets inces- 
santly from the vegetable and mineral worlds into the 
mineral world again. It may be compared to an eddy in 
a river, which may retain its shape for an indefinite length 
of time, though no one particle of the water of the stream 
remains in it for more than a brief period 

But there is this peculiarity about the human eddy, 
that a large portion of the particles of matter which How 
into it have a much more complex composition than the 
particles which flow out of it. To speak in what is not 

• irether a metaphor, the atoms which enter the body 

. f«>r the most part, piled up in large heaps, and tumble 
down int<» small heaps before they leave it. The force 
which they ><-t \v<'<\ in thus tumbling down, i> the BOUTCe 

of the active p< >wers 1 4 the i trganism. 

195. Organs of Motion, — Th«*s«' active powers are chiefly 



132 ELEMENTARY PHYSIOLOGY. 

manifested in the form of motion — movement, that is, either 
of part of the body, or of the body as a whole, which last 
is termed locomotion. 

The organs which produce total or partial movements 
of the human body are of three kinds : cells exhibiting 
amoeboid movements, cilia, and muscles. 

The amoeboid movements of the white corpuscles of the 
blood have been already described, and it is probable that 
similar movements are performed by many other simple 
cells of the body in various regions. 

The amount of movement which each cell is thus capa- 
ble of giving rise to may appear perfectly insignificant ; 
nevertheless, there are reasons for thinking that these 
amoeboid movements are of great importance to the econ- 
omy, and may under certain circumstances be followed by 
very notable consequences. 

196. Action of the Cilia. — Cilia are filaments of ex- 
tremely small size, attached by their bases to, and indeed 
growing out from, the free surfaces of epithelial cells (see 
341) ; there being in most instances very many (thirty-, for 
instance), but, in some cases, only a few cilia on each cell. 
In some of the lower animals, cells may be found possess- 
ing only a single cilium. They are in incessant waving 
motion, so long as life persists in them. Their most com- 
mon form of movement is that each cilium is suddenly bent 
upon itself, becomes sickle-shaped instead of straight, and 
then more slowly straightens again, both movements, how- 
ever, being extremely rapid and repeated about ten times 
every second. These two movements are of course antag- 
onistic ; the bending drives the water or fluid in which 
the cilium is placed in one direction, while the straighten- 
ing drives it back again. Inasmuch, however, as the bend- 
ing is much more rapid than the straightening, the force 
expended on the water in the former movement is greater 
than in the latter. The total effect of the double move- 
ment therefore is to drive the fluid in the direction towards 



INSTRUMENTS OF MOTION. 183 

which the ciliura is beni ; thai is, of course, if the cell on 
which the cilia are placed is fixed It' the eel] be floating 
free, the effect is to drive or row the cell backwards ; for 
their movements may continue even for some time after 
the epithelial cell, with which they are connected, is de- 
tached from the body. And nol only do the movements 
i t the cilia thus go on independently of the rest of the 
body, but they cannot be controlled by the action of the 
nervous system. Each cilium seems to be composed of 

tractili substance, and the cause of its movement would 
appear to be the alternate contraction and relaxation of its 
opposite rides along its whole length or at its base only; 
but why these alternations take place is unknown. 

Although no other part of the body has any control 

over the cilia, and though, so far as we know, they have 

DO direct communication with one another, yet their action 
i- directed toward.- a common end — the cilia, which cover 

tensive surfaces, all working in such a manner as to 

eep whatever lies upon that surface in one and the same 
direction. Thus, the cilia which are developed upon the 
epithelial cells, which line the greater pari of the nasal 
cavities and the trachea, with its ramifications, tend to 
drive the mucus in which they work, outwards. 

In addition to the air-] 5, cilia are found, in the 

human body, in th3 ventricles of the brain, and in one or 

two other localities ; hut the pari which they play in man 
i- insignificant in comparison with their function in the 
lower animals, among many of which they become the 

- of locomotion. 

197. Muscular Contraction. — Muscles (is) are accumu- 
lations of fibres, each fibre having a definite strud 
which is differenl in the striated and unstriated kinds (see 
ire "hound up by fibrous (or connective) 

lie with blood-vessels, <•'<•.. into small bundles; and 
these bundles in similarly bound up together in 

various waj to form mtu rarious shapes and 



184 ELEMENTARY PHYSIOLOGY. 

sizes. Every fibre has the power, under certain condi- 
tions, of shortening in length, while it increases its other 
dimensions, so that the absolute volume of the fibre re- 
mains unchanged. This power is called muscular contrac- 
tility / and whenever, in virtue of this power, a muscular 
fibre contracts, it tends to bring its two ends, with what- 
ever may be fastened to them, together. 

The condition which ordinarily determines the contrac- 
tion of a muscular fibre is a change of state in a nerve- 
fibre, which is in close anatomical connection with the 
muscular fibre. The nerve-fibre is thence called a motor 
fibre, because, by its influence on a muscle, it becomes the 
indirect means of producing motion (317). 

Muscle is a highly-elastic substance. It contains a 
large amount of water (about as much as the blood), and 
during life has a clear and semi-transparent aspect. 

198. Rigor Mortis. — When subjected to pressure in the 
perfectly fresh state, and after due precautions have been 
taken to remove all the contained blood, striated muscle 
(355) yields a fluid which undergoes spontaneous coagula- 
tion at ordinary temperatures. At a longer or shorter time 
after death this coagulation takes place within the muscles 
themselves. They become more or less opaque, and, losing 
their previous elasticity, set into hard, rigid masses, which 
retain the form which they possess when the coagulation 
commences. Hence the limbs become fixed in the position 
in which death found them, and the body passes into the 
condition of what is termed the " death-stiffening," or rigor 
mortis. After the lapse of a certain time the coagulated 
matter liquefies, and the muscles pass into a loose and flaccid 
condition, which marks the commencement of putrefaction. 

It has been observed that the sooner rigor mortis sets 
in, the sooner it is over ; and, the later it commences the 
longer it lasts. The greater the amount of muscular exer- 
tion, and consequent exhaustion before death, the sooner 
rigor mortis sets in. 






INSTRUMENTS OF MOTION. 185 

199. Composition of Muscle. — Rigor mortis evidently 
presents some analogies with the coagulation of the blood, 
and the substance which thus coagulates within the fibre 

yosin, or muscle-clot, as it is sometimes called), is in 
many respects not unlike fibrin. It forms at least the 
greater part of the substanee which may be extracted from 
muscle by dilute acids, and is called syntonin [see 167). 
Besides myosin, muscle contains other varieties of proteid 
material about which we at present know little ; a variable 
quantity of fat; certain inorg*anic saline matters, phosphates 
and potash being, as is the case in the red blood-corpuscles, 
in excess ; and a large number of substances existing in 
small quantities, and often classed together as " extrac- 
tives." Some of these extractives contain nitrogen; the 
most important of this class is creatin^ a crystalline body 
which is supposed to be the chief form in which nitro- 
genous waste matter leaves the muscle on its way to be- 
come urea. 

The other class of extractives contains bodies free from 
nitrogen. Perhaps the most important of these is lactic 

K which seems always to be formed when a muscle con- 
tracts, or when it enters into rigor mortis. For it is a 
curious fact that a muscle when at rest has a neutral or 
alkaline reaction, as shown by testing it with litmus, but 
IxM-omes acid when it has been contracting for some time 
or become rigid by death. 

Most muscles are of a deep-red color ; this is due in part 
totbe blood remaining in their vessels ; but only in part, 
for each fibre (into which no capillary enters) has a reddish 

>rof its own, like a blood-corpuscle, but fainter. And 
color i- probably due to the fibre possessing a small 
quantity of thai same haemoglobin in which the blood- 
corpuscles arc so rich. 

200. Attachment of Muscles. — Muscles may be con- 
reniently divided into two groups, according to the man- 
ner iu which the ends of their fibres are fastened — into 



186 ELEMENTARY PHYSIOLOGY. 

muscles not attached to solid levers, and muscles attached 
to solid levers. 

201. Muscles not attached to Solid Levers. — Under this 
head come the muscles which are appropriately called hol- 
low muscles, inasmuch as they inclose a cavity or surround 
a space ; and their contraction lessens the capacity of that 
cavity, or the extent of that space. 

The muscular fibres of the heart, of the blood-vessels 3 
of the lymphatic vessels, of the alimentary canal, of the 
urinary bladder, of the ducts of the glands, of the iris of 
the eye, are so arranged as to form hollow muscles. 

In the heart the muscular fibres are of the striated kind, 
and their disposition is exceedingly complex. The cavities 
which they inclose are those of the auricles and ventricles; 
and, as we have seen, the fibres, when they contract, do so 
suddenly and together. 

The iris of the eye is like a curtain, in the middle of 
which is a circular hole. The muscular fibres are of the 
smooth or unstriated kind {see -355), and they are disposed 
in two sets : one set radiating from the edges of the hole 
to the circumference of the curtain ; and the other set ar- 
ranged in circles, concentrically with the aperture. The 
muscular fibres of each set contract suddenly and together, 
the radiating fibres necessarily enlarging the hole, the cir- 
cular fibres diminishing it. 

In the alimentary canal the muscular fibres are also of 
the unstriated kind, and they are disposed in two layers ; 
one set of fibres being arranged parallel with the length 
of the intestines, while the others are disposed circularly, 
or at right angles to the former. 

As has been stated above (190), the contraction of these 
muscular fibres is successive ; that is to say, ail the mus- 
cular fibres, in a given length of the intestines, do not con- 
tract at once, but those at one end contract first, and the 
others follow them until the whole series have contracted. 
As the order of contraction is, naturally, always the same, 



MECHANISM OF BODILY MOVEMENT. 1ST 

from the upper towards the lower end, the effect of this 
peristaltic contraction is, as we have seen, to force any 
matter, contained in the alimentary canal, from its upper 
towards its lower extremity. The muscles of the walls of 
the duets of the glands have a substantially similar ar- 
rangement. In these cases the contraction of each fibre is 
less sudden, and lasts longer than in the case of the heart. 

Section II. — Mechanism of Bodily Movement. 

202. Muscles attached to Definite Levers. — The great 
majority of the muscles in the body are attached to dis- 
tinct levers, formed by the bones, the minute structure of 
which is explained in Chapter XI I. In such bones as are 
ordinarily employed as levers, the osseous tissue is ar- 
ranged in the form of a shaft (Fig. 56, 6), formed of a very 
dense and compact osseous matter, but often containing a 
great central cavity (b) which is filled with a very delicate 
vascular and fibrous tissue loaded with fat called marrow. 
Towards the two ends of the bone, the compact matter of 
the shaft thins out, and is replaced by a much thicker but 
looser sponge-work of bony plates and fibres, which is 
termed the c<incellous tissue of the bene. The surface even 
of this part, however, is still formed by a thin sheet of 
denser bone. 

At least one end of each of these bony levers is fash- 
ioned into a smooth, articular surface, covered with car- 
til age, which enables the relatively fixed end of the bone 
to play upon the corresponding surface of some other bone 
with which it is said to be articulated, or, contrariwise, 
allows that other bone to move upon it. 

Ii is one or other of these extremities which plays the 
part of fulcrum when the bone i- in use as a lever. 

Thus, in the accompanying figure (Fig. 57), of the 

bones of the upper extremity, with the attachment of the 

muscle to the shoulder-blade and to one of the two 

l><>ijes of the forearm called the radius, P indicates the 



188 



ELEMENTARY PHYPICLCGY. 



point of action of the power (the contracting muscle) upon 
the radius. 

But, to understand the action of the bones, as levers, 
properly, it is necessary to possess a knowledge of the 







Fig. 56. 
Longitudinal Section of the Shaft of a Human Femur or Thigh-bone. 

a, the head, which articulates with the haunch -bone ; &, the medullary cavity, and 
d, the dense bony substance of the shaft ; c, the part which enters into the knee-joint, 
articulating with the shin-bone, or tibia. 



MECHANISM OF BODILY MOVEMENT. 



189 



different kinds of levers, and be able to refer the various 
combinations o( the bones to their appropriate lever-classes. 
A lever is a rigid bar, one part of which is absolutely 
or relatively fixed, while the rest is free to move. Some 
one point of the movable part of the lever is set in motion 




Fig. 57. 

Tiif. Coses OF the Uppeb Extremity, w-rrn the Biceps MrPCLE. 

The two tendons by which this muscle is attached to the scapula arc soon at a ; P 
indi sates the attachment of the muscle to the radius, and hence tin point of action of 
the power; F, the fulcrum, the lower end of the humerus on which the upper end of 
the radii^ [together with the ulna) moves; W, the weight (of the hand;. 

by a force, in order to communicate more or less of that 
motion to another point of the movable part, which pre- 
sents a resistance to motion in the shape of a weight or 
other obstacle. 

203. Three Orders of Levers, — Three kinds of levers 
are enumerated by mechanicians, the definition of each 
kind depending upon the relative positions of the point of 

port, or fulcrum ; of the point which bears the resist* 

' iffkt) i r other obstacle to be overcome bv the force ; 

and of the point to which the force, or power employed to 

ercome the obstacle, is a; iplied. 

It" the fulcrum be placed between the power and the 

weight, bo that, when the power - be the lever in motion, 

the weight and tin* power describe arcs, the concavities 



190 



ELEMENTARY PHYSIOLOGY. 



of which are turned towards one another, the lever is said 
to be of the first order. (Fig. 58.) 

If the fulcrum be at one end, and the weight be be- 
tween it and the power, so that w r eight and power describe 
concentric arcs, the weight moving through the less space 
when the lever moves, the lever is said to be of the second 
order. (Fig. 59.) 

And if, the fulcrum being still at one end, the power be 
between the weight and it, so that, as in the former case, 



P / ■ P F 





Fig. 58. 



Fig. 59. 



Fig. GO. 



The upper portions of the three figures represent the three kinds of levers; the 
lower portions, the. foot, when it takes the character of each kind. W, weight or re- 
sistance ; F, fulcrum ; P, power. 



the power and weight describe concentric arcs, but the 
power moves through the less space, the lever is of the 
third order. (Fig. 60.) 

204. Levers of the First Order. — In the human body, 
the following parts present examples of levers of the first 
order. 

(a) The skull in its movements upon the atlas, as fid- 
crum. 

(b) The pelvis in its movements upon the heads of the 
thigh-bones, as fulcrum. 

(c) The foot, when it is raised, and the toe tapped on 
the ground, the ankle-joint being fulcrum. (Fig. 58.) 

The positions of the weight and of power are not given 
in either of these cases, because they are reversed accord- 



MECHANISM OF BODILY MOVEMENT. 101 

inir to circumstances. Thus, when the face is being de- 
pressed, the power is applied in front, and the weight to 
the back part, of the skull; but, when the (ace is being 
the power is behind and the weight in front. The 

like is true of the pelvis, according as the body is bent for- 
ward, or backward, upon the legs. Finally, when the toes, 
in the action of tapping, strike the ground, the power is at 
the heel, and the resistance in the front of the foot. But, 
when the toes are raised to repeat the act, the power is in 
front, and the weight, or resistance, is at the heel, being, 
in fact, the inertia and elasticity of the muscles and other 
parts of the back of the leg. 

But, in all these cases, the lever remains one of the first 
class, because the fulcrum, or fixed point on which the 
lever turns, remains between the power and the weight, 
or resistance. 

205. Levers of the Second Ordsr. — The following are 
three examples of levers of the secon ] order: 

('/> The thigh-bone of the leg, which is bent up towards 
the body and not used, in the action of hopping. 

For, in this case, the fulcrum is at the hip-joint. The 
p<»wer (which may be assumed to be furnished by the thick 
muscle x of the front of the thigh) acts upon the knee-cap ; 
and the position of the weight is represented by that of the 
.ire of gravity of the thigh and leg, which will lie sonic- 
where between the end of the knee and the hip. 

(ft) A rib when depressed by the re -tns muscle 2 of the 
►men, in expiration. 

Here the fulcrum lies where the rib is articulated with 

the spine; the power i.^ at th<* sternum — virtually the op- 

of the rib; and the resistance to be overcome 

the two. 

to tli*- hannch-bono and below to the 
tng ligament with toe 

■Miiimi wall on each aide of the middle Him. It 
toatt. ot «»t* tli- pehii below (Pig, \ 



192 ELEMENTARY PHYSIOLOGY. 

(c) The rising of the body upon the toes, in standing 
on tiptoe, and in the first stage of making a step forwards. 
(Fig. 59.) 

Here the fulcrum is the ground on which the toes rest ; 
the power is applied by the muscles of the calf to the heel 
(Fig. 4, I.) ; the resistance is so much of the weight of the 
body as is borne by the ankle-joint of the foot, which, of 
course, lies between the heel and the toes. 

206. Levers of the Third Order. — Three examples of 
levers of the third order are : 

(a) The spine, head, and pelvis, considered as a rigid 
bar, which has to be kept erect upon the hip -joints. 
(Fig. 4.) 

Here the fulcrum lies in the hip-joints ; the weight is 
at the centre of gravity of the head and trunk, high above 
the fulcrum ; the power is supplied by the extensor, or 
flexor, muscles of the thigh, and acts upon points compara- 
tively close to the fulcrum. (Fig. 4, 2 and II.) 

(b) Flexion of the forearm upon the arm by the biceps 
muscle, when a weight is held in the hand. 

In this case, the weight being in the hand and the ful- 
crum at the elbow-joint, the power is applied at the point 
of attachment of the tendon of the biceps, close to the lat- 
ter. (Fig. 57.) 

(c) Extension of the leg on the thigh at the knee-joint. 
Here the fulcrum is the knee-joint ; the weight is at 

the centre of gravity of the leg and foot, somewhere be- 
tween the knee and the foot ; the power is applied by the 
muscles in front of the thigh (Fig. 4, 2), through the liga- 
ment of the knee-cap, or patella, to the tibia, close to the 
knee-joint. 

207. Each Kind represented in the Foot. — In studying 
the mechanism of the body, it is very important to recol- 
lect that one and the same part of the body may represent 
each of the three kinds of levers, according to circum- 
stances. Thus it lias been seen that the foot may, under 



MECHANISM OF BODILY MOVEMENT. 193 

some circumstances, represent a lever of the first, in others, 
of tin 1 second order. But it may become a lever of the 
third order, as when one dances a weight, resting upon the 
toes, up and down, by moving only the foot. In this case, 
the fulcrum is at the ankle-joint, the weight is at the toes, 
and the power is furnished by the extensor muscles at the 
front of the leg (Fig. 4, 1), which are inserted between the 
fulcrum and tin 4 weight. (Fig. 50.) 

208. Joints. — It is very important that the levers of the 
body should not slip, or work unevenly, when their move- 
ments are extensive, and to this end they are eonnected 
together in such a manner as to form strong and definitely- 
arranged joints or articulations. 

Joints may be classified into imperfect and perfect. 

209. Imperfect Joints are those in which the conjoined 
levers (bones or cartilages) present no smooth surfaces, 
capable of rotatory motion, to one another, but are con- 
nected by continuous cartilages, or ligaments, and have 
only so much mobility as is permitted by the flexibility of 
t lie joining substance. 

Examples of such joints as these are to be met with in 
the vertebral column — the flat surfaces of the bodies of the 
vertebra^, being connected together by thick plates of very 
elastic fibro-cartilage, which confer upon the whole column 
considerable play and springiness, and vet preyent any 

it amount of motion between the several vertebrae. In 
the pelvis (see Plate, Fig. VI.), the pubic bones are united 
to each other in front, and the iliac bones to the sacrum 
behind, by fibrous or cartilaginous tissue, which allows of 

Only a Blight play, and so gives the pelvis a little more 
ticity than it would have if it were all one bone. 

210. Perfect Joints. — In all perfect joints, the opposed 
bony surfaces which move upon one another are covered 

with Cartilage, and between theni is placed a sort of sac, 

which lines these cartilages, and, to a certain extent, forma 
the side-walls of the joint; and which, secreting a small 
IS 



194 



ELEMENTARY PHYSIOLOGY. 



quantity of viscid, lubricating fluid — the sy?iovia — is called 
a synovial membrane. 

211. Structure and Working of Joints. — The opposed 
surfaces of these articular cartilages, as they are called, 
may be spheroidal, cylindrical, or pulley-shaped ; and the 
convexities of the one answer, more or less completely, to 
the concavities of the other. 

Sometimes, the two articular cartilages do not come 
directly into contact, but are separated by independent 
plates of cartilage, which are termed inter-art icidar. The 
opposite faces of these inter-articular cartilages are fitted 
to receive the faces of the proper articular cartilages. 




Fig. SI. 

A Section of the Hip-Joint taken through the Acetabulum o* Articulab 
Cup of the Pelvis and the Middle of the Head and Neck of the Thigh- 
bone. 

L. T 7 ., ligamentum teres, or round ligament. The spaces marked with an inter- 
rupted line ( ) represent the articular cartilages. The cavity of the synovial 

membrane is indicated by the dark line between, and, as is shown, extends along- the 
neck of the femur beyond the limits of the cartilage. The peculiar shape of the pelvis 
causes the section to hare the remarkable outline shown in the cut. This will be intel- 
ligible if compared with Fig. VI. in the Plate. 



MECHANISM OF BODILY MOVEMENT. 



105 



While these coadapted surfaces and synovial mem- 
branes provide for the fijpe molality of the bones entering 
into a joint, the nature and extent of their motion are de- 
fined, partly by the forms of the articular surfaces, and 
partly by the disposition of the ligaments, or firm, fibrous 
eords, which pass from one bone to the other. 




:rrr>iN.\L and Vi.ktk al Si;, tion T1IB0U6H tiik Ki.now-Jorvr. 

H^ huu alnji; TV.. • muscle which eactendfl the arm: Hi., tho 

muscle which flexed it. 



212. Ball-and-Socket Joints. — As respects the nature of 

the articular surfaces, j< >iut > may he what are called ball- 

eket joints, when the spheroidal Burface furnished by 

one bone plays in a cup furnished by another. In tl 

the motion of the firmer bone may take place in any di- 

tion, Jmt the extent of the motion depends upon the 

pe of the cup — being very greal when the cup is shal- 

iall in proportion Bfl it is deep. The shoulder 



196 ELEMENTARY PHYSIOLOGY. 

is an example of a ball-and-socket joint with a shallow 
cup ; the hip, of such a joint w r ith a deep cup (Fig. 61). 

213. Hinge -Joints are single or double. In the former 
case, the nearly cylindrical head of one bone fi£s into a 
corresponding socket of the other. In this form of hinge- 
joint the only motion possible is in the direction of a plane 
perpendicular to the axis of the cylinder, just as a door can 
only be made to move round an axis passing through its 
hinges. The elbow is the best example of this joint in 
the human body, but the movement here is limited, because 
the olecranon, or part of the ulna which rises up behind 
t^e humerus, prevents the arm being carried back behind 
the straight line ; the arm can thus be bent to, or straight- 
ened, but not bent back (Fig. 62). The knee and ankle 
present less perfect specimens of a single hinge-joint. 

A double hinge-joint is one in which the articular sur- 
face of each bone is concave in one direction, and convex 
in another, at right angles to the former. A man seated in 
a saddle is tt articulated " with the saddle by such a joint. 
For the saddle is concave from before backwards, and con- 
vex from side to side, while the man presents to it the 
concavity of his legs astride, from side to side, and the 
convexity of his seat, from before backwards. 

The metacarpal bone of the thumb is articulated with 
the bone of the wrist, called trapezium, by a double hinge- 
joint. 

214. Pivot-Joints. — A pivot-joint is one in w^bich one 
bone furnishes an axis or pivot, on which another turns ; 
or itself turns on its own axis, resting on another bone. A 
remarkable example of the former arrangement is afforded 
by the atlas and axis, or two uppermost vertebra? of the 
neck (Figs. 63, 64). The axis possesses a vertical peg, the 
so-called odontoid process (S), and at the base of the peg are 
two obliquely-placed, articular surfaces (a). The atlas is 
a ring-like bone, with a massive thickening on each side. 
The inner side of the front of the ring plays round the 



MECHANISM OF BODILY MOVEMENT. 



197 



neck of the odontoid peg, and the under surfaces of the 
lateral masses glide over the articular faces on each side 
o( the base o( the peg. A strong- ligament passes between 
the inner sides o( the two lateral masses of the atlas, and 
keeps the hinder side o( the neck o( the odontoid peg 
in its place (Fig. 63). By this arrangement, the atlas is 
enabled to rotate through a considerable angle either way 
upon the axis, without any danger of falling forwards or 
backwards — accidents which would immediately destroy 
life by crushing the spinal marrow. 




Fi<;. 63. 



Fig. 04. 



Fiir. 68. — The atlas viewed from above: a a. upper articular surfaces of its lateral 

- lor the condyles of the skull; b. the peg of the axis vertebra. 
Fig. <'4. — Side view of the axis vertebra: (/. articular surface for the lateral mass 
of the atlas ; 6, peg or odontoid process. 



The lateral masses of the atlas have, on their upper 
faces, concavities (Fig. 63, a) into which the two con- 
vex, occipital condyles of the skull fit, and in which they 
play upward and downward. Thus the nodding of the 
bead is effected by the movement of the skull upon the 
atlas; while, in turning the head from side to side, the 
skull does not move upon the atlas, but the atlas slides 

round the odontoid peg of the axis vertebra. 

The Beoond kind of pivot-joint is seen in the forearm. 
If the elbow and forearm, as far as the wrist, are made to 

• upon a table. :md the elbow is kept finely fixed, the 

hand can nevertheless be freely rotated so that either the 

mi, or the b:ek, i> turned directly upward-. When the 



198 



ELEMENTARY PHYSIOLOGY. 



palm is turned upwards, the attitude is called supination 
(Fig. 65); when the back, pronation (Fig. 66). 

The forearm is composed of two bones ; one, the ulna, 
which articulates with the humerus at the elbow by the 
hinge-joint already described, in such a manner that it can 
move only in flexicn and extension (see 216), and has no 
power of rotation. Hence, when the elbow and wrist are 
rested on a table, this bone remains unmoved. 

But the other bone of the forearm, the radius, has its 



jb- 




Fig. 66. 



Fig. 65. 



Fig. 65. — The bones of the right forearm in supination. 
Fig. 66 — in pronation. — //., humerus ; is?., radius ; J7., ulna. 

small upper end shaped like a very shallow cup with thick 
edges.* The hollow of the cup articulates with a sphe- 
roidal surface furnished by the humerus ; the lip of the 
cup, with a concave depression on the side of the ulna. 
The large lower end of the radius bears the hand, and 






i\ 



MECHANISM OF BODILY MOVEMENT. 



190 



has, on the side next the ulna, a concave surface, which 
articulates with the convex side o( the small lower end of 
that bone. 

Thus the upper end of the radius turns on the double 
surface, furnished to it by the pivot-like ball of the hume- 
rus, and the partial cup oi' the ulna : while the lower end 
of the radius can rotate round the surface furnished to it 
bv the lower end o{ the ulna. 

In supination, the radius lies parallel with the ulna, 
with its lower end to the outer side of the ulna (Fig. G5). 
In pronation, it is made to turn on its own axis above, 
and round the ulna below, until its lower half crosses the 
ulna, and its lower end lies on the inner side of the ulna 
(Fig. 66). 

215. The Ligaments. — The ligaments which keep the 
mobile surfaces of bones together are, in the case of ball- 




Fi<. 

The vertebral column in the upper perl of tin- neck laid open, to show—*/, the 

do; //. toe broad ligameni which extends from the rail 

. n of the <x-rij.it:ii foramen :il<>m: the hinder hoes <>r the bodies of the vertebra; it 

rt mroogh, ana the ent ends turned back to sb moot which 

e jH.int of the "odontoid* \»j, with the front margin of the ocdpttal fbra- 

I 



and-sockel joints, Strang fibrous capsules which surround 
the joint on all sides, hi hinge-joints, on the other hand, 
th" ligamentous tissue is chieflj accumulated, in the hn\u 



200 ELEMENTARY PHYSIOLOGY. 

of lateral ligaments, at the sides of the joints. In some 
cases ligaments are placed within the joints, as in the 
knee, where the bundles of fibres which cross obliquely 
between the femur and the tibia are called crucial liga- 
ments ; or, as in the hip, where the round ligament passes 
from the bottom of the socket or acetabulum of the pelvis 
to the ball furnished by the head of the femur (Fig. 61). 

Again, two ligaments pass from the apex of the odon- 
toid peg to either side of the margins of the occipital fora- 
men, i. e., the large hole in the base of the skull, through 
which the spinal cord passes to join the brain ; these, from 
their function in helping to stop excessive rotation of the 
skull, are called check ligaments (Fig. 67, a). 

In one joint of the body, the hip, the socket or acetabu- 
lum (Fig. 61) fits so closely to the head of the femur, and 
the capsular ligament so completely closes its cavity on all 
sides, that the pressure of the air must be reckoned among 
the causes which prevent dislocation. This has been proved 
experimentally by boring a hole through the floor of the 
acetabulum, so as to admit air into its cavity, when the 
thigh-bone at once falls as far as the round and cap- 
sular ligaments will permit it to do, showing that it was 
previously pushed close up by the pressure of the exter- 
nal air. 

216. Th3 Various Movements of Joints, — The different 
kinds of movement which the levers thus connected are 
capable of performing, are called flexion and extension ; 
abduction and adduction / rotation and circumduction. 

A limb is flexed, when it is bent ; extended, when it is 
straightened out. It is abducted, when it is drawn away 
from the middle line ; adducted, when it is brought to the 
middle line. It is rotated, when it is made to turn on its 
o;vn axis; circumducted, when it is made to describe a 
conical surface by rotation round an imaginary axis. 

No part of the body is capable of perfect rotation like 
a wheel, for the simple reason that such motion would 



MECHANISM OF BODILY MOVEMENT. 20] 

necessarily tear all the vessels, nerves, muscles, etc., which 
unite it with other parts. 

217. How these Movements are effected. — Any two 
bones united by a joint may be moved one upon another 
in, at fewest, two different directions. In the case of a pure 
hinge-joint, these directions must be opposite and in the 
same plane; but, in all other joints, the movements may 
be in se\eral directions and in various planes. 

In the case of a pure hinge-joint, the two practicable 
movements — viz., flexion and extension — may be effected 
by means of two muscles, one for either movement, and 
running from one bone to the other, but on opposite sides 
of the joint. When either of these muscles contracts, it 
will pull its attached ends together, and bend or straighten, 
18 the case may be, the joint towards the side on which it 
is placed. Thus at the elbow-joint there is, in front of the 
joint, the biceps muscle, running from the arm to the fore- 
arm (jB/., Fig. f>"2); when this contracts it pulls its two 
ends together, and so flexes the forearm on the arm. At 
the back of the joint there is the triceps (jTa); when this 
contracts, it straightens or extends the forearm on the arm. 

In the other extreme form of articulation — the ball-and- 
socket joint — movement in any number of planes may be 
effected, by attaching muscles in corresponding number 
and direction, on the one hand, to the bone which affords 
the socket, and, on the other, to that which furnishes the 
head. ( Srcumduction will be effected by the combined and 
successive contraction of these muscles. 

218, Tendons and their Functions. — It usually happens 
that the bone to which one end of a muscle is attached is 
absolutely or relatively stationary, while that to which the 
other is fixed is movable. In this case, the attachment to 
the stationary bone is termed the origin, that to the mov- 
able bone the insertion, of the muscle. 

The fibres <>t* muscles are sometimes fixed diiafectly into 
(he parts which serve ;»^ their origins and insertions: but, 



202 ELEMENTARY PHYSIOLOGY. 

more commonly, strong cords or bands of fibrous tissue, 
called tendons, are interposed between the muscle proper 
and its place of origin or insertion. When the tendcns 
play over hard surfaces, it is usual for them to be sepa- 
rated from these surfaces by sacs containing fluid, which 
are called bursce ; or even to be invested by synovial 
sheaths, i. e., quite covered for some distance by a syno- 
vial bag forming a double sheath very much in the same 
way that the bag of the pleura covers the lung and the 
chest-wall. 

Usually, the direction of the axis of a muscle is that of 
a straight line joining its origin and its insertion. But in 
some muscles, as the superior oblique muscle of the eye, 
the tendon passes over a pulley formed by ligament, and 
completely changes its direction before reaching its inser- 
tion. [See 235). 

Again, there are muscles which are fleshy at each end, 
and have a tendon in the middle. Such muscles are called 
digastric, or two-bellied. In the curious muscle which 
pulls down the lower jaw, and specially receives this name 
of digastric, the middle tendon runs through a pulley con- 
nected with the hyoid bone ; and the muscle, which passes 
downwards and forwards from the skull to this pulley, after 
traversing it, runs upwards and forwards, to the lower jaw 
(Fig. 68). 

Section III. — Movements of Locomotion. 

219. Walking. — We may now pass from the considera- 
tion of the mechanism of mere motion to that of locomo- 
tion. 

When a man who is standing erect on both feet pro- 
ceeds to walk, beginning with the right leg, the body is 
inclined so as to throw the centre of gravity forward ; and, 
the right foot being raised, the right leg is advanced for 
the length of a step, and the foot is put down again. In 
the mean while, the left heel is raised, but the toes of the 



MOVEMENTS OF LOCOMOTION. 203 

left foot have not left the ground when the right foot has 

reached it, so that there is no moment at which both feet 
are oft' the ground. For an instant, the legs form two 
sides of an equilateral triangle, and the centre of the body 
Consequently lower than it was when the legs wore par- 
allel and close together. 

. The left foot, however, has not been merely dragged 

away from its first position, but the muscles of the calf, 

having come into play, act upon the foot as a lever of the 

ond order, and thrust the body, the weight of which 




fto. 

The Course of the Dioabtbic Mim le. 

terior belly; IV, its ant-rior belly ; between the tw<> is the tendon passing 
thr«mL r h its pulley connected with //y.. the hyoid bone. 

}ta largely on the left astragalus, upwards, forwards, and 
t<> the right side. The momentum thus communicated to 
the body causes it. with the whole right leg, to describe an 
air ovr the right astragalus, on which that log rests below. 
The centre of the body consequently ri>os to its former 
height a- the right log becomes vertical, and descends 
again a- tin- right leg, in it< turn, inclines forward. 

When the left fool ha- left the ground, the body 18 sup- 
ported on the right leg, and i- well in advance of the left 
30 that, without any further muscular exertion, the 

left foot swings forward like a pendulum, and i> carried by 

it- own momentum beyond the right fool, to the position 

in which it completes tl 1 step. 



204 ELEMENTARY PHYSIOLOGY. 

220. Economy of Force in Walking. — When the inter- 
vals of the steps are so timed that each swinging leg comes 
forward into position for a new step without any exertion 
on the part of the w^alker, walking is effected with the 
greatest possible economy of force. And, as the swinging 
leg is a true pendulum — the time of vibration of which de- 
pends, other things being alike, upon its length (sl^prt 
pendulums vibrating more quickly than long ones) — it fol- 
lows that, on the average, the natural step of shcrt-legged 
people is quicker than that of long-legged ones. 

221. Running and Jumping. — In running, there is a 
period when both legs are off the ground. The legs are 
advanced by muscular contraction, and the lever action of 
each foot is swift and violent. Indeed, the action of each 
leg resembles, in violent running, that which, when both 
legs act together, constitutes a jump, the sudden extension 
of the legs adding to the impetus, which, in slow walking, 
is given only by the feet. 

Section IV. — Vocal Movements, 

222. Conditions of the Production of Voice. — Perhaps 
the most singular motor apparatus in the body is the 
larynx, by the agency of which voice is produced. 

The essential conditions of the production of the human 
voice are : 

a. The existence of the so-called vocal chords. 

b. The parallelism of the edges of these chords, without 
which they will not vibrate in such a manner as to give 
out sound. 

c. A certain degree of tightness of the vocal chords, 
without which they will not vibrate quickly enough to 
produce sound. 

d. The passage of a current of air between the parallel 
edges of the vocal chords of sufficient power to set the 
chords vibrating. 

223. The Larynx. — The larynx is a short tubular box 



VOCAL MOVEMENTS. 205 

opening above into the bottom of the pharynx, and below 
into the top of the trachea. Its framework is supplied by 
certain cartilages more or less movable on each other, and 
these are connected together by joints, membranes, and 
muscles. Across the middle of the larynx is a transverse 
partition, formed by two folds of the lining mucous mem- 
brane, stretching from either side, but not quite meeting 
in the middle line. They thus leave, in the middle line, a 




Pre. 89. 

Diaemm of the larynx, the thyroid cartilage (77/>bein<r supposed to be transparent, 
and allowinsr the riuht arytenoid cartilage {Ar.) vocal chords ( P.), and thyro-aiyte- 
!< id maade i Th.AX the upper part of the cricoid cartilage (<>.). and the attachment 
of the epiglottis if,'/*.), to he seen; C.th., the right crico-thyroid muscle; Tr., the 
trachea : Uy., the hyoid bone. 

chink or slit, running from the front to the back, called 
the glottis. The two edges of this slit are not round and 
flabby, but sharp and, so to speak, clean cut; they are also 
strengthened by a quantity of elastic tissue, the fibres of 
which arc disposed lengthways in them. These sharp free 
gres of the glottis arc the so-called vocal chords or vocal 
ligaments. 

224 The Carriages of the larynx. — The thyroid ear- 
tilage (Fig. 69, 77L) is a broad plate of gristle bent upon 

If int<» a V-shape, and BO disposed that the point of the 



208 



ELEMENTARY PHYSIOLOGY. 



V is turned forwards, and constitutes what is commonly 
called "Adam's apple." Above, the thyroid cartilage is 
attached by ligament and membrane to the hyoid bone 
(Fig. G9, Si/-)' Below and behind, its broad sides are 
produced into little elongations or horns, which are articu- 
lated by ligaments with the outside of a great ring of car- 
tilage, the cricoid (Fig. 69, 6V.), which forms, as it were, 
the top of the windpipe. 

The cricoid ring is much higher behind than in front, 
and a gap, filled up by membrane only, is left between its 




Fig. 70. 

A Vertical and Transverse Section through the Larynx, the hinder Half 
of which is removed. 
Ep., epiglottis ; Th., thyroid cartilage ; a, cavities called the ventricles of larynx 
above the vocal ligaments ( V. ) ; x the right thyro-arytenoid muscle cut across ; O., 
the cricoid cartilage. 

upper edge and the lower edge of the front part of the 
thyroid, when the latter is horizontal. Consequently, the 
thyroid cartilage, turning upon the articulations of its 
horns with the hinder part of the cricoid, as upon hinges, 
can be moved up and down through the space occupied by 
this membrane. When it moves downwards, the distance 



t 



VOCAL MOVEMENTS. 



207 



hot ween the front pari of the thyroid cartilage and the 
back of the cricoid is necessarily increased ; and, when it 
moves back again to the horizontal position, diminished. 
There is, on each side, a large muscle, the cricothyroid^ 
which passes from the outer side of the cricoid cartilage 
obliquely upwards and backwards to the thyroid, and pulls 
the latter down (Fig. 69, C.th.). 

Perched side by side, upon the upper edge of the back 
part of the cricoid cartilage are two small irregularly- 
shaped but, roughly speaking, pyramidal cartilages, the 
arytenoid cartilages (Fig. 71, Ary.). Each of these is 




^Lr./u 



Fi«;. 71. 
Thf. Pabtb surrounding the Glottis partially dissected and viewed from 

ABOVE. 

77/.. the thyroid cartilage; O., the cricoid cartilage; J'., the edges of the vocal 
ligaments bounding the glottis; Ari/. % ttte arytenoid cartilages; 77/. .1. thyroaryte- 
noid; i '.</./.. lateral crico-ary tenoid ; C.a.p., posterior crico-arytenoid ; Ar.j>.\ posterior 
id muscles. 



articulated by its base with the cricoid cartilage by means 
of a shall >w joint which permits of very varied movements, 
and especially allows the front portions of the two aryte- 
in id cartilages to approach, or to recede from, each other. 
225. Attachment of the Vocal Ligaments. — It is to the 
fore pad of one of these arytenoid carl ilages thai the hinder 



208 



ELEMENTARY PHYSIOLOGY. 



end of each of the two vocal ligaments is fastened ; and 
they stretch from these points horizontally across the cav- 
ity of the larynx, to be attached, close together, in the 
reentering angle of the thyroid cartilage rather lower than 
half-way between its top and bottom. 

226. The Muscles of the larynx. — Now, when the aryt- 
enoid cartilages diverge, as they do when the larynx is in 





Fig. 74. 

Fig 72. — View of the human larynx from above as ectually seen by the aid of the 
instrument called the laryngoscope. 

Fig. 73. — In the condition when voice is being produced. 

Figs. 74, 75. — At rest, when no voice is produced. 

e. Epiglottis (foreshortened). 

c.v. The vocal chords. 

c.v.s. The so-called false vocal chords, folds of mucous membrane lying above the 
real vocal chords. 

a. Elevation caused by the arytenoid cartilages. 

s.ic. Elevations caused by small cartilages connected with the arytenoids. 

I. Eoot of the tongue. 



a state of rest, it is evident that the aperture of the glof t's 
will be V-shaped, the point of the V being forwards, and 
the base behind. 

For, in front, or in the angle of the thyroid, the two 
vocal ligaments are fastened permanently close together, 
whereas, behind, their extremities will be separated as far 



VOCAL MOVEMENTS. 209 

as the arytenoids, to which they are attached, are sepa- 
rated from each other. Under these circumstances a cur- 
rent of air passing through the glottis produces no sound, 
the parallelism of the vocal chords being wanting; whence 
it is that, ordinarily, expiration and inspiration take place 
quietly. Passing from one arytenoid cartilage to the 
other, at their posterior surfaces are certain muscles called 
the posterior arytenoid (Fig. 71, Ar.p.). There are also two 
sets of muscles connecting each arytenoid with the cricoid, 
and called from their positions respectively the posterior 
and lateral cricoarytenoid (Fig. 71, C.a.p., C.a.l). By 
the more or less separate or combined action of these mus- 
cles, the arytenoid cartilages and, consequently, the hinder 
ends of the vocal chords attached to them, may be made 
to approach or recede from each other, and thus the vocal 
chords rendered parallel or the reverse. 

We have seen that the crico-thyroid muscle pulls the 
thyroid cartilage down, and thus increases the distance 
between the front of the thyroid and the back of the 
cricoid, on which the arytenoids are seated. This move- 
ment, the arytenoids being fixed, must tend to pull out 
the vocal chords lengthways, or, in other words, to tighten 
them. 

Running from the reentering angle in the front part of 
the thyroid, backward, to the arytenoids, alongside the 
vocal chords (and indeed embedded in the transverse folds, 
of which the chords are the free edges) are two strong 
muscles, one on each side (Fig. 71, Th.A?), called the 
thyroarytenoid. The effect of the contraction of these 
muscles is to pull up the thyroid cartilage after it has been 
depressed by the crico-thyroid muscles, and consequently 
ii the vocal chords. 

Thus the parallelism (#) of the vocal chords is deter 
mined chiefly by the relative distance from each other of 

the arytenoid carl ilages j the tension (c) of the vocal chords 

determined chiefly by the upward or downward move- 

I ! 



210 



ELEMENTARY PHYSIOLOGY. 



ment of the thyroid cartilage ; and both these conditions 
are dependent on the action of certain muscles. 

227. Notes— Range and Quality of Voice. — The current 
of air whose passage sets the chords vibrating is supplied 
by the movements of expiration, which, when the chords 
are sufficiently parallel and tense, produce that musical 
note which constitutes the voice, but otherwise give rise 
to no audible sound at all. 

Other things being alike, the musical note will be low 
or high, according as the vocal chords are relaxed or tight- 



\~-- 




a 


FlG. 


i 

A 

76. 





Diagram of a model illustrating the action of the levers and muscles of the larynx. 
The stand and vertical pillar represent the cricoid and arytenoid cartilages, while the 
rod (be), moving on a pivot at c, takes the place of the thyroid cartilage ; a b is an 
elastic band representing the vocal ligament. Parallel with this runs a cord fastened 
at one end to the rod b c, and, at the other, passing over a pulley to the weight B. This 
represents the thyro-arytenoid muscle. A cord attached to the middle of b c, and pass- 
ing over a second pulley to the weight A, represents the crico-thyroid muscle. It is 
obvious that, when the bar (b c) is pulled down to the position of c d, the elastic band 
(a b) is put on the stretch. 

ened ; and this again depends upon the relative predomi- 
nance of the contraction of the crico-thyroid and thyro- 
arytenoid muscles. For when the thyro-arytenoid muscles 
are fully contracted, the thyroid cartilage will be pulled up 
as far as it can go, and the vocal chords will be rendered 
relatively lax ; while, when the crico-thyroid muscles are 
fully contracted, the thyroid cartilage will be depressed as 
much as possible, and the vocal chords will be made more 
tense. 






VOCAL MOVEMENTS. 211 

The ran (ft of any voice depends upon the difference of 
tension which can be given to the vocal chords, in these 
two positions oi the thyroid cartilage. Accuracy of sing- 
ing depends upon the precision with which the singer can 
voluntarily adjust the contractions of the thyro-arytenoid 
and crico-thyroid muscles — so as to give his vocal chords 
the exact tension at which their vibration will yield the 
notes required. 

The quality of a voice — treble, bass, tenor, etc. — on 
the other hand, depends upon the make of the particular 
larynx, the primitive length of its vocal chords, their elas- 
ticity, the amount of resonance of the surrounding parts, 
and so on. 

Thus, men have deeper notes than boys and women, 
because their larynxes are larger and their vocal chords 
longer — whence, though equally elastic, they vibrate less 
swiftly. 

228. Speech. — Speech is voice modulated by the throat, 
tongue, and lips. Thus, voice may exist without speech ; 
and it is commonly said that speech may exist without 
voice, as in whispering. This is only true, however, if the 
title of voice be restricted to the sound produced "by the 
vibration of the vocal chords; for, in whispering, there is 
a sort of voice produced by the vibration of the muscular 
walls of the lips which thus replace the vocal chords. A 
whisper is, in fact, a very low whistle. 

229. Vowel and Consonant Sounds. — The modulation 
of the voice into speech is effected by changing the form 
of the cavity of the mouth and nose, by the action of the 
muscles which move the walls of those parts. 

ThllS, if the pure VOWel sounds — 

A'ce in he), A (as in hay), A! (as in '///), 
(as in or), O (as in oh), OO (as in cool), 

are pronounced successively, it will be found that they 
may be all formed oul of the Bound produced by <« con- 



212 ELEMENTARY PHYSIOLOGY. 

tinuous expiration, the mouth being kept open, but the 
form of its aperture, and the extent to which the lips are 
thrust out or drawn in so as to lengthen or shorten the 
distance of the orifice from the larynx, being changed for 
each vowel. It will be narrowest, with the lips most 
drawn back, in E, widest in A\ and roundest, with the 
lips most protruded, in O. 

Certain consonants also may be pronounced without 
interrupting the current of expired air, by modification of 
the form of the throat and mouth. 

Thus the aspirate, H, is the result of a little extra ex- 
piratory force — a sort of incipient cough. S and Z, Sh 
and e/^as in jugular = G soft, as in gentry), Th, i, i?, F, 
V, may likewise all be produced by continuous currents of 
air forced through the mouth, the shape of the cavity of 
which is peculiarly modified by the tongue and lips. 

All the vocal sounds hitherto noted so far resemble one 
another, that their production does not involve the stop- 
page of the current of air which traverses either of the 
modulating passages. 

But the sounds of M and iV^can only be formed by 
blocking the current of air which passes through the 
mouth, while free passage is left through the nose. For 
ill/", the mouth is shut by the lips ; for JST, by the application 
of the tongue to the palate. 

The other consonantal sounds of the English language 
are produced by shutting the passage through both nose and 
mouth ; and, as it were, forcing the expiratory vocal cur- 
rent through the obstacle furnished by the latter, the char- 
acter of which obstacle gives each consonant its pecu- 
liarity. Thus, in producing the consonants B and P, the 
mouth is shut by the lips, which are then forced open in 
this explosive manner. In jTand D, the mouth-passage is 
suddenly barred by the application of the point of the 
tongue to the teeth, or to the front part of the palate ; 
while in JTand G (hard, as in go) the middle and back of 






VOCAL MOVEMENTS. 213 

the tongue are similarly forced against the back part of the 
palate. 

230. Speaking-Machines. — An artificial larynx maybe 
constructed by properly adjusting elastic bands, which take 
the place of the vocal chords ; and, when a current of air is 
forced through these, due regulation of the tension of the 
bands will give rise to all the notes of the human voice. 
A- each vowel and consonantal sound is produced by the 
modification of the length and form of the cavities, which 
lie over the natural larynx, so, by placing over the artificial 
buynx chambers to which any requisite shape can be given, 
the various letters may be sounded. It is by attending to 
these facts and principles that various speaking-machines 
have been constructed. 

231. Tongueless Speech. — Although the tongue is cred- 
ited with the responsibility of speech, as the "unruly mem- 
ber/' and undoubtedly takes a very important share in its 
production, it is not absolutely indispensable. Hence, the 
apparently fabulous stories of people who have been en- 
abled to speak, after their tongues had been cut out by 
the cruelty of a tyrant, or persecutor, may be quite true. 

♦ Some years ago I had the opportunity of examining a 

person, whom I will call Mr. R , whose tongue had been 

removed as completely as a skillful surgeon could perform 
the operation. When the mouth was widely opened, the 
truncated face of the stump of the tongue, apparently cov- 
ered with new mucous membrane, w T as to be seen, occupy- 
ing a position as far back as the level of the anterior pil- 
lars of the fauces. The dorsum of the tongue waa visible 
with difficulty; but I believe T could discern some of the 

rircumvallate papilla* upon it. None of these were visible 

upon the amputated part of the tongue, which had been 
preserved in spirits; and which, so far as I could judge, 

Was aboul two and a half inched long. 

When hi- mouth was open, Mr. R could advance his 

tongue no farther than the position in which 1 saw it ; but 



214 ELEMENTARY PHYSIOLOGY. 

he informed me that, when his mouth was shut, the stump 
of the tongue could be brought much more forward. 

Mr. R 's conversation was perfectly intelligible ; and 

such words as think, the, cow, hill, were well and clearly 
pronounced. But tin became fin ; tack, fack or pack ; 
toll, pool ; dog, thog ; dine, vine ; dew, thew ; cat, cat/; 
mad, mdf ; goose, gooth ; big, pig, bich, pich, with a gut- 
tural ch. 

In fact, only the pronunciation of those letters the for- 
mation of which requires the use of the tongue was af- 
fected ; and, of these, only the two which involve the 

employment of its tip were absolutely beyond Mr. R 's 

power. He converted all t's, and d's, into fs, p^s, v^s, or 
til's. Th was fairly given in all cases ; s and sh, I and r, 
with more or less of a lisp. Initial g*s and tfs were good ; 
but final g*s were all more or less guttural. In the former 
case, the imperfect stoppage of the current of air by the 
root of the tongue was of no moment, as the sound ran on 
into that of the following vowel ; while, when the letter 
was terminal, the defect at once became apparent. 



CHAPTER VIII. 

SENSATIONS AND SENSORY ORGANS. 

Section I. — Reflex Action — Groups of Sensations. 

232. Efferent and Afferent Nerves. — The agent by which 
all the motor organs (except the cilia) described in the pre- 
ceding chapter are set at work, is muscular fibre. But, in 
the living body, muscular fibre is made to contract only by 
a change which takes place in the motor or efferent nerve, 
which is distributed to it. This change, again, is effected 
only by the activity of the central nervous organ, with 
which the motor nerve is connected. The central organ is 






KEFLEX ACTION— GROUPS OF SENSATIONS. 215 

thrown into activity immediately, or ultimately, only by 
the influence of changes which take place in the molecular 
condition of nerves, called sensory of afferent, which are 
connected, on the one hand, with the 1 central organ, and, 
on the ether hand, with some other part of the body. 
Finally, the alteration ot* the afferent nerve is itself pro- 
duce 1 only by changes in the condition of the part of the 
body, with which it is connected; which changes usually 
result from external impressions. 

233. Conveyance of Molecular Impressions. — Thus the 
at majority (if not the whole) of the movements of the 

body and of its parts, are the effect of an influence (tech- 
nically termed a stimulus or irritation) applied directly, or 
indirectly, to the ends of afferent nerves, and giving rise to 
a molecular change, which is propagated along their sub- 
Btance to the central nervous organ with which they are 
connected. The molecular activity of the afferent nerve 
communicates itself to the central organ, and is then trans- 
mitted along the motor nerves, which pass from the central 
organ to the muscles affected. And, when the disturbance 
in the molecular condition of the efferent nerves reaches 
their extremities, it is communicated to the muscular 
fibres, and catises their particles to take up a new position, 
so that each fibre shortens and becomes thicker. 

234. Reflex Action, Sensations and Consciousness. — 
Such a series of molecular changes as that just described 
is called a reflex action — the disturbance caused by the 
irritation being as it were reflected back, along the motor 
Qerves, to the muscles. 

A reflex action, strictly so called, takes place without 
our knowing any thing about it, and hundreds of such 
actions are going on continually in our bodies without on, 

og aware of them. Bui it very frequently happens that 
we learn that something is going on, when a stimulus 
affects our afferent nerves, by having what we call a feel- 
ing or * nscUion, We class sensations along with emotions, 



210 ELEMENTARY PHYSIOLOGY. 

and volitions, and thoughts, under the common head of 
states of consciousness. But what consciousness is, we 
know not ; and how it is that any thing so remarkable as 
a state of consciousness comes about, as the result of irri- 
tating nervous tissue, is just as unaccountable as any other 
ultimate fact of Nature. 

235. Subjective Sensations. — Sensations are of very va- 
rious degrees of definiteness. Some arise within ourselves, 
we know not how or where, and remain vague and unde- 
finable. Such are the sensations of uncomfortableness, or 
faintness, of fatigue, or of restlessness. We cannot assign 
any particular place to these sensations, which are very 
probably the result of affections of the afferent nerves in 
general brought about bj T the state of the blood, or that 
of the tissues in which they are distributed. And how- 
ever real these sensations may be, and however largely 
they enter into the sum of our pleasures and pains, they 
tell us absolutely nothing of the external world. They 
are not only diffuse, but they are also subjective sensa- 
tions. 

236. The Muscular Sense. — What is termed the mus- 
cular sense is less vaguely localized than the preceding, 
though its place is still incapable of being very accurately 
defined. This muscular sensation is the feeling of resist- 
ance which arises when any kind of obstacle is opposed to 
the movement of the body, or of any part of it ; and it is 
something quite different from the feeling of contact or 
even of pressure. 

Lay one hand flat on its back upon a table, and rest a 
disk of card-board a couple of inches in diameter upon the 
ends of the outstretched fingers ; the only result will be a 
sensation of contact — the pressure of so light a body being 
inappreciable. But put a two-pound weight upon the card- 
board, and the sensation of contact will be accompanied, 
or even obscured, by the very different feeling of pressure. 
Up to this moment the fingers and arm have rested upon 



REFLEX ACTION— GROUPS OF SENSATIONS. 217 

the table; but now let the hand be raised from the table, 
and another new feeling will make its appearance — that 
of resistance to effort* This feeling comes into existence 
with the exertion of the muscles which raise the arm, and 
is the consciousness of that exertion given to us by the 
muscular sense. 

Any one who raises or carries a weight, knows well 
enough that he has this sensation; but he may be greatly 
puzzled to say where he has it. Nevertheless, the sense 
itself is very delicate, and enables us to form tolerably 
accurate judgments of the relative intensity of resistances. 
Persons who deal in articles sold by weight are constantly 
enabled to form very precise estimates of the weight of 
such articles, by balancing them in their hands ; and, in 
this case, they depend in a great measure upon the mus- 
cular sense. 

237. The Higher Senses. — In a third group of sensa- 
tions, each feeling, as it arises, is assigned to a definite 
part of the body, and is produced by a stimulus applied to 
that part of the body ; but the bodies, or forces, w 7 hich are 
competent to act as stimuli, are very various in character* 
Such are the sensations of touchy which is restricted to the 
integument covering the surface, and to some portions of 
the membranes lining the internal cavities of the body ; 
and of taste and smell, which are similarly confined to 
< < rtain regions of the mucous membrane of the mouth and 
nasal cavities. 

Any portion of the body to which a sensation is thus 

ricted is called a sensory organ. 

And lastly, in a fourth group of sensations, each feeling 
requires foi it- production the application of a single kind 

stimulus to a very specially-modified pari of the integu- 
ment. The latter serves as an intermediator between the 
physical agent of tin- Bensation and the sensory nerve, 
which is to convey to the brain the impulse necessary to 

ike in it thai State of consciousness which we call the 



218 ELEMENTARY PHYSIOLOGY. 

sensation. Such are the sensations of sight and hearing. 
The physical agents which can alone awaken these sensa- 
tions (under natural circumstances) are light and sound. 
The modified parts of the integument, which alone are 
competent to intermediate between these agents and the 
nerves of sight and hearing, are the eye and the ear. 

233. General Plan of a Sensory Organ. — In every sen- 
sory organ it is necessary to distinguish the terminal ex- 
pansion of the afferent or sensory nerve, and the structures 
which intermediate between this expansion and the phys- 
ical agent which gives rise to the sensation. 

And in each group of special sensations there are cer- 
tain phenomena which arise out of the structure of the 
organ, and others which result from the operation of the 
central apparatus of the nervous system upon the materials 
supplied to it by the sensory organ. 

Section II. — Touch, Taste, and Smell. 

239. The Sense of Touch.— The sense of Touch (in- 
cluding that of heat and cold) is possessed, more or less 
acutely, by all parts of the free surface of the body, and 
by the walls of the mouth and nasal passages. 

Whatever part possesses this sense consists of a mem- 
brane (integumentary or mucous) composed of a deep layer 
made up of fibrous tissue, containing a capillary network 
and the ultimate terminations of the sensory nerves ; and 
of a superficial layer consisting of epithelial or epidermic 
cells, among which are no vessels. 

Wherever the sense of touch is delicate, the deep layer 
is not a mere flat expansion, but is raised up into multi- 
tudes of small, close-set, conical elevations (see Fig. 40), 
w 7 hich are called papillce. In the skin, the coat of epithe- 
lial or epidermic cells does not follow the contour of these 
papillae, but dips down between them and forms a toler- 
ably even coat over them. Thus, the points of the papillae 
are much nearer the surface than the general plane of the 



TOUCH TASTE, AND SMELL. 219 

deep layer whence these papillae proceed. Loops of vessels 
enter the papillae, and the 1 line ultimate terminations of 
the sensory nerve-fibres distributed to the skin terminate in 
them, but in what way has not been thoroughly made out. 

In certain cases, the delicate fibrous sheath, or neuri- 
lemma^ of the nerve, which enters the papilla, enlarges in 
the papilla into an oval swelling, which is called a tactile 

jniscle (see 357). These corpuscles are found in the 
papilla? of those localities which are endowed with a very 
delicate sense of touch, as in the tips of the fingers, the 
point of the tongue, etc. 

240. Functions of Epithelium. — It is obvious, from what 
has been said, that no direct contact takes place between 
a body which is touched and the sensory nerve — a thicker 
or thinner layer of epithelium, or epidermis, being situated 
between the two. In fact, if this layer is removed, as 
when a surface of the skin has been blistered, contact with 
the raw surface gives rise to a sense of pain, not to one of 
touch properly so called. Thus, in touch, it is the epider- 
mis, or epithelium, which is the intermediator between the 
nerve and the physical agent, the external pressure being 
transmitted through the horny cells to the subjacent ends 
of the nerves, and the kind of impulse thus transmitted 
must be modified by the thickness and character of the 
cellular layer, no less than by the forms and number of the 
papillae. 

241. Varying Tactile Sensibility. — Certain very curious 
phenomena appertaining to the sense of touch are prob- 
ably due to these varying anatomical arrangements. Not 
only is tactile sensibility to a single impression much duller 
in some parts than in others — a circumstance which might 

readily accounted for by the differenl thickness of the 

epidermic layer — but the power of distinguishing d uble 

Qtdtaneoua impressions is very different. Thus, if the 

ends of a pair of compasses (which should be blunted with 

pointed pieces of cork) are separated by only one-tenth or 



220 ELEMENTARY PHYSIOLOGY. 

one-twelfth of an inch, they will be distinctly felt as two, 
if applied to the tips of the fingers ; whereas, if applied to 
the back of the hand in the same way, only one impression 
will be felt ; and, on the arm, they may be separated for a 
quarter of an inch, and still only one impression will be 
perceived. 

Accurate experiments have been made in different parts 
of the body, and it has been found that two points can be 
distinguished by the tongue, if only one-twenty-fourth of an 
inch apart ; by the tips of the fingers if one-twelfth of an 
inch distant ; while they may be one inch distant on the 
cheek, and even three inches on the back, and still give 
rise to only one sensation. 

242. The Sense of Warmth or Cold. — The feeling of 
warmth, or cold, is the result of an excitation of sensory 
nerves distributed to the skin, which are probably distinct 
from those which give rise to the sense of touch. And it 
would appear that the heat must be transmitted through 
the epidermic or epithelial layer, to give rise to this sensa- 
tion ; for, just as touching a naked nerve, or the trunk of a 
nerve, gives rise only to pain, so heating or cooling an ex- 
posed nerve, or the trunk of a nerve, gives rise not to a 
sensation of heat or cold, but simply to pain. 

Again, the sensation of heat, or cold, is relative rather 
than absolute. Suppose three basins be prepared, one 
filled with ice-cold water, one with water as hot as can be 
borne, and the third with a mixture of the two. If the 
hand be put into the hot-water basin, and then transferred 
to the mixture, the latter wall feel cold ; but, if the hand be 
kept a while in the ice-cold water, and then transferred to 
the very same mixture, it will feel warm. 

Like the sense of touch, the sense of warmth varies in 
delicacy in different parts of the body. 

The cheeks are very sensitive, more so than the lips ; 
the palms of the hands are more sensitive to heat than 
their backs. Hence a washer-woman holds her flat-iron to 



TOUCH, TASTE, AND SMELL. 



221 



her cheek to test the temperature, and one who is cold 
spreads the palms of his hands to the fire, 

243. The Sense of Taste— the Tongue. — The organ of 
the sense of TASTE is the mucous membrane which covers 
the tongue, especially its bark part, and the hinder part of 
the palate. Like that of the skin, the deep, or vascular, 







mi m, 




-f./u 



Fig. 77. 

tfle m"t~th widely opened to bhow tut. tohqcx and palate. 

the uvula: 7fe~ the ton-il between the anterior and posterior pillars of the 
p^ drcomvaliate papifls ; /•'.//.. fangiform papilla?. The minute filiform pa- 

Sillae eorer the Interspace* between these. Onthenghl side the tongue Is partially 
-how the course of the filaments of the giosaopharyng I III. 



layer of the mucous membrane of the tongue is rais< d hj) 
into papillae, but these are large, separate, and have sepa- 
rate coats of epithelium. Towards the tipofthe tongue 
they arc for the mosl part elongated and pointed, and are 
called filiform ; over the rest of the surface of the tongue, 



222 ELEMENTARY PHYSIOLOGY. 

these are mixed with other larger papillae, with broad ends 
and narrow bases, called fungiform y but, towards its root, 
there are a number of large papillae, arranged in the figure 
of a V, with its point backwards, each of which is like a 
fungiform papilla surrounded by a wall. These are the 
circum vallate papillae (Fig. 77, C.jx). The larger of these 
papillae have subordinate small ones upon their surfaces. 
They are very vascular, and they receive nervous filaments 
from two sources, the one the nerve called glossopharyngeal, 
the other the gustatory, which is a branch of the fifth nerve. 
(See 330.) The latter chiefly supplies the front of the 
tongue, the former its back and the adjacent part of the 
palate ; and there is reason to believe that it is the latter 
region which is more especially the seat of the sense of 
taste. 

The great majority of the sensations we call taste, how- 
ever, are in reality complex sensations, into which smell 
and even touch largely enter. When the sense of smell is 
interfered with, as when the nose is held tightly pinched, 
it is very difficult to distinguish the taste of various ob- 
jects. An onion, for instance, the eyes being shut, may 
then easily be confounded with an apple. 

244. Smell— Mechanism of the Nostrils. — The organ of 
the sense of Smell is the delicate mucous membrane which 
lines a part of the nasal cavities, and is distinguished from 
the rest of the mucous membrane of these cavities — firstly, 
by possessing no cilia ; secondly, by receiving its nervous 
supply from the olfactory, or first, pair of cerebral nerves, 
and not, like the rest of the mucous membrane, from the 
fifth pair. 

Each nostril leads into a spacious nasal chamber, sepa- 
rated, in the middle line, from its fellow of the other side, 
by a partition, or septum, formed partly by cartilage and 
partly by bone, and continuous with that partition which 
separates the two nostrils one from the other. Below, 
each nasal chamber is separated from the cavity of the 



TOUCH, TASTE, AND SMELL. 223 

mouth by a floor, the bony palate (Figs. 78, 79, 80) ; and, 
when this bony palate comes to an end, the partition is 
continued down to the root of the" tongue by a fleshy cur- 
tain, the soft palate, which has been already described. 
The soft palate and the root of the tongue together con- 
stitute, under ordinary circumstances, a movable partition 
between the mouth and the pharynx, and it will be ob- 
served that the opening of the larynx, the glottis, lies be- 
hind the partition; so that, when the root of the tongue is 
applied close to the soft palate, no passage of air can take 
place between the mouth and the pharynx. But in the 
upper part of the pharynx above the partition are the two 
hinder openings of the nasal cavities (which are called the 
posterior nares) separated by the termination of the sep- 
tum ; and through these wide openings the air passes, with 
great readiness, from the nostrils along the lower part of 
each nasal chamber to the glottis, or in the opposite direc- 
tion. It is by means of the passages thus freely open 
to the air, that we breathe, as we ordinarily do, with the 
mouth shut. 

Each nasal chamber rises, as a high vault, far above the 
level of the arch of the posterior nares — in fact, about as 
high as the depression of the root of the nose. The upper- 
most and front part of its roof, between the eyes, is formed 
by a delicate horizontal plate of bone, perforated, like a 

e, by a great many small holes, and thence called the 
cribriform plate (Fig. 80, CV.). It is this plate (with the 
membranous structures which line its two faces) alone 
which, in this region, separates the cavity of the nose from 
that which contains the brain. The olfactory lobes which 
arc directly connected with, and form indeed a part of, the 
brain, enlarge at their ends, and their broad extremities 
resl upon the upper side of the cribriform plate; sending 
immense numbers of delicate filaments, the olfactory nerves, 
through it to the olfactory mucous membrane (Fig. 79). 

On each wall of the septum this inncons membrane 



224 



ELEMENTARY PHYSIOLOGY. 



forms a flat expansion, but on the side walls of each* nasal 
cavity it follows the elevations and depressions of the 
inner surfaces of what are called the upper and middle 




Fig. 78. 




Fig. 79. 
Vertical Longitudinal Sections op the Nasal Cavity. 

Fig. 78 represents the outer wall of the left nasal cavity. 

Fig-. 70 represents the right side of the middle partition, or septum (Sp.\ of the 
nose, which forms the inner wall of the right nasal cavity. 7, the olfactory nerve and 
its branches ; V, branches of the fifth nerve ; Pa., the palate, which separates the 
nasal cavity from that of the mouth ; S.T.. the superior turbinal bone ; M.T., the mid- 
dle turbinal ; I. ZI, the inferior turbinal. The letter I is placed in the cerebral cavity ; 
and the partition on which the olfactory lobe rests, and through which the filaments 
of the olfactory nerves pass, is the cribriform plate. 



TOUCH, TASTE, AND SMELL. 225 

turbinal, or spongy bones. These bones are called spongy 
because the interior of each is occupied by air cavities 
separated from each other by very delicate partitions 
only, and communicating with the nasal cavities. Hence 
the bones, though massive-looking, are really exceedingly 
light and delicate, and fully deserve the appellation of 
spongy (Fig. SO). 

There is a third light scroll-like bone distinct from these 
two, and attached to the maxillary bone, which is called 
the inferior turbinal, as it lies lower than the other two, 
and imperfectly separates the air passages from the propel 
olfactory chamber (Fig. 78). It is covered by the ordinary 
ciliated mucous membrane of the nasal passage, and re- 
ceives no filaments from the olfactory nerve (Fig. 78). 

245, The Beason of "Sniffing." — From the arrange- 
ments which have been described, it is clear that, under 
ordinary circumstances, the gentle inspiratory and expira- 
tory currents will flow along the comparatively wide, 
direct passages afforded by so much of the nasal chamber 
as lies below the middle turbinal; and that they will 
hardly move the air inclosed in the narrow interspace 
between the septum and the upper and middle spongy 
bones, which is the proper olfactory chamber. 

If the air-currents are laden with particles of odorous 
matter, they can only reach the olfactory membrane by 
diffusing themselves into this narrow interspace ; and, if 
there be but few of these particles, they will run the risk 
of not reachinir the olfactory mucous membrane at all, 
unless the air in contact with it he exchanged for some of 
the odoriferous air. Hence it is that, when we wish to 
perceive a faint odor more distinctly, wo sniff, or snuff up 
the air. Each sniff is a sudden inspiration, the effect of 
which must reach the air in the olfactory chamber at the 

ie time as, or eveil before, it affectfl thai at the nostrils; 
and thus must tend to draw a little air out of that cham- 
ber from behind. At the Baine time, or immediately after- 
15 



226 



ELEMENTARY PHYSIOLOGY. 



wards, the air sucked in at the nostrils entering with a 
sudden vertical rush, part of it must tend to flow directly 
into the olfactory chamber, and replace that thus drawn 
out. 

The loss of smell which takes place in the course of a 
severe cold may, in part, le due to the swollen state of 



Cr. 




.%7h 



A Transverse and Vertical Section of the Osseous Walls of the Nasal 
Cavity taken nearly through the Letter I in the foregoing Figure. 

O., the cribriform plate; S.T.. 3f.T„ the chambered superior and middle tnrbinal 
bones on which and on the septum (Sp.) the filaments of the olfactory nerve are dis- 
tributed : /. 21, the inferior turbinal bone : PL, the palate ; An., the Antrum or cham- 
ber which occupies the greater part of the maxillary bone and opens into the nasal 
cavity. 

the mucous membrane which covers the inferior turbinal 
bones, which thus impedes the passage of odoriferous air 
to the olfactory chamber. 



Section III. — The Mechanism of Hearing. 

246, Structure of the Ear. — The Ear, or organ of the 
sense of Hearing, is very much more complex than either 
of the sensory organs yet described. It will be useful to 
distinguish the essential parts of this complicated appara- 
tus from certain other parts, which, though of great assist- 



THE MECHANISM OF HEARING. 227 

anoe to the sense, are not absolutely necessary, and there- 
fore may be called accessory. 

The essential parts, on either side of the head, consist, 
substantially, of two peculiarly-formed membranous bags, 
called, respectively, the membranous labyrinth and the 

fa media of thi cochlea. Both these bags are lodged 
in cavities which they do not completely fill, situated in 
the midst of a dense and solid mass of bone (from its 
hardness called petrosal), which forms a part of the tem- 
poral beme, and enters into the base of the skull. 

Each bag- is filled with a fluid, and is also supported in 
a fluid which fills the cavity in which it is lodged. In the 
interior of each bag, certain small, mobile, hard bodies 
are contained; and the ultimate filaments of the auditory 
nerves are so distributed upon the walls of the bags that 
their terminations must be knocked by the vibrations of 
these small hard bodies, should any thing set them in 
motion. It is also quite possible that the vibrations of the 
fluid contents of the sacs may themselves suffice to affect 
the filaments of the auditory nerve; but, however this 
may b?, any such effect must be greatly intensified by the 
cooperation of the solid particles. 

In bathing in a tolerably smooth sea, on a rocky shore, 
the movement of the little waves as they run backwards 
and forwards is hardly felt by any one lying down ; but, in 
bathing on a sandy and gravelly beach, the pelting of the 
showers of little stones and sand, which are raised and let 
fall by each wavelet, makes a very definite impression on 
the nerves of the skin. 

Now, the membrane on which the ends of the auditory 
nerv<*< are spread out i> virtually a sensitive beach, and 

waves, which by themselves would not be felt, are readily 
; ivrd when they raise and l«-t i'all hard particles. 

B >tb th<--<- membranous bags are lined by an epithe- 
lium. 

The auditory Qerve, aft t passing through the deu<<' 



228 



ELEMENTARY PHYSIOLOGY. 



bone of the skull, is distributed to certain regions of each 
bag, where its ultimate filaments come into peculiar con- 
nection with the epithelial lining. The epithelium itself, 
too, at these spots becomes specially modified. In certain 
parts of the membranous labyrinth, for instance, the epi- 
thelium connected with the terminations of the auditory 
nerve is produced into long, stiff, slender, hair-like pro- 




Fig. 81. 

diagram to illustrate the termination of the auditory nerve in ak 

Ampulla. 

I. The epithelium of the ampulla. II. The membranous wall of the ampulla on 
which the epithelium rests. 

a, a filament of the auditory nerve running through the wall of the ampulla and 
breaking up into a fiDe net-work (b) in the epithelium ; c, epithelium cell with long, 
stiff, hair-like filament, d (this cell is supposed by some to be directly continuous with 
the nerve net-work) ; e. cells, not bearing filaments, placed by the side of and support- 
ing the filament-bearing cells ; J\ a deeper layer of smaller cells. 



cesses (Fig. 81, c?), which project into the fluid filling the 
bag, and which therefore are readily affected by any vibra- 
tion of that fluid, and communicate the impulse to the ends 
of the nerve. In certain other parts of the same labyrinth 
these hairs are scanty or absent, but their place is supplied 
by minute angular particles of calcareous sand (called oto- 
conia or otolithes), lying free in the fluid of the bag. 
These, driven by the vibrations of that fluid, strike the 
epithelium and so affect the auditory nerve. 



THE MECHANISM OF HEARING. 229 

In the scala media of the cochlea, minute, rod -like 
bodies, called the fibres of Curti, and which are peculiarly 
moditied cells of the epithelial lining of the scala, appear 
to serve the same object. 

247. The Vestibule,— For simplicity's sake, the mem- 
branous labyrinth and the scala media have hitherto been 
spoken of as if they were simple bags ; but this is not the 
case, each bag having a very curious and somewhat com- 
plicated form. (Figs. 82 and 83.) 




Ttte Membranous Labyrinth, twice tiie Natural Size. 

Ft. the Utriculus. or part of the vestibular sac. into which the semicircular canals 
open: A. A. A. the ampulla-: P. A., anterior vertical semicircular canal: P. V.. pos- 
terior vertical semicircular canal ; H.. horizontal semicircular canal. The sacculus is 
not seen, as in the position in which the labyrinth is drawn the sacculus lies behind 
the utriculus. The white circles on the ampulla? of the posterior vertical and horizon- 
tal canals indicate the cut ends of the branches of the auditory nerve ending in tnose 
ampullae : the branches to the ampulla of the anterior vertical canal are seen in the 
space embraced by the canaL as is also the branch to the utriculus. 

This form is also followed to a certain extent by the 
bonv casing r >f the cavity in which each is lodged. Tims 
the membranous labyrinth is surrounded by a bony laby- 
rinth^ and the scala media is only a part of an intricate 
-tincture called the cochlea. The bony labyrinth and 

hlea, with all the parts inside each, constitute together 
what is failed the internal ear. 

The membranous labyrinth (Fig. 82) has the figure of 
an oval vestibular sac, consisting of two parts, the one 
called utriculus, the other sacculus hemisphericus. The 
hoop-like semicircular canals open into the utriculus. They 

arc three in number, and. two being vertical, arc called the 

anterior | P.A.) and posterior (P. VI) vertical semicircular 



230 ELEMENTARY PHYSIOLOGY. 

canals / while the third, lying outside, and horizontally, is 
termed the external horizontal semicircular canal (If). 
One end of each of these canals is dilated into what is 
called an ampulla (A). 

It is upon the walls of these ampullae and those of the 
vestibular sac that the branches of the auditory nerve are 
distributed. 

In each ampulla the nervous filaments may be traced to 
a transverse ridge caused by a thickening of the connective 
tissue which forms the walls of the canal (as well as of all 
other parts of the membranous labyrinth), and also by 
a thickening of the epithelium. Some of the epithelium 
cells are here prolonged into the fine hair-like processes 
described above. It is probable that these cells are 
specially connected with the terminations of the nerve- 
filaments. 

In the vestibule are similar but less marked ridges, or 
patches ; here, however, the hair-like prolongations of the 
epithelium cells are absent or scanty, but, instead, otolithes 
are found in the fluid. 

The fluid which fills the cavities of the semicircular 
canals and utriculus is termed endolymph. That which 
separates these delicate structures from the bony chambers 
in which they are contained is the perilymph. Each of 
these fluids is little more than water. 

248. The Cochlea. — In the scala media l of the cochlea 
the primitive bag is drawn out into a long tube, which is 
coiled two and a half times on itself into a conical spiral, 
and lies in a much wider chamber of corresponding form, 
excavated in the petrous bone in such a way as to leave a 
central column of bony matter called the modiolus. The 
scala media has a triangular transverse section (Fig. 83), 
being bounded above and below by the membranous walls 

1 I employ this term as the equivalent of canalis eochlearis. The true nature and 
connections of these parts have only recently been properly worked out, and the ac- 
count now given will be found to be somewhat different from that in the first edition 
of this work. See particularly the explanatioo of Fig-. 84. 






THE MECHANISM OF HEARING. 231 

which converge internally and diverge externally. At their 
convergence, the walls are fastened to the edge of a thin 
plate of bone, the lamina spiralis (£.£., Fig. 83), which 
winds round the modiolus. At their divergence they are 
fixed to the wall of the containing bony chamber, which 
thus becomes divided into two passages, communicating 
at the summit of the spire, but elsewhere separate. These 
two passages are called respectively the scala tympani 
and scala vestibuli^ and are filled with perilymph. 

The scala media, which thus lies between the other two 
Bcalae, opens below, or at the broad end of the cochlea, by 
a narrow duct into the sacculus hemisphericus, but at its 
opposite end terminates blindly. (Fig. 8T.) 




Fk, 

A Section through tiik Axis Of Tin; OoOKLBA, magnified three Diameters. 

ScJf., scala media : St T". scala vmibuli : .v. 7.. scala tympani: L.S., lamina 
sjiira.is: JA/.. bony axis, or modiolus, round which the scalar are wound; C.N., coch- 
lear nerve. 

That branch of the auditorv nerve which goes to supply 
the cochlea, niters the broad base of the central column 
or modiolus, and there divides into branches, which, 
spreading out in a spiral fashion in channels excavated 

in the bony tissue, are distributed to the lamina spiralis 
throughout Lt8 Whole length. They do UOi end here; but 
in any Section of the lamina spiralis (Fig. 83, L.S.) they 
maybe found running outwards from the central column 

across the lamina towards the angle of the scala media, 
in which indeed thev become finallv lost. 



232 



ELEMENTARY PHYSIOLOGY. 



The upper wall of the scala media, that which separates 
it from the scala vestibuli, is called the membrane of 



ScaJF 



ScaM 




Fig. 84. 
A Section through that Wall of the " Scala Media m of the Cochlea which 

LIES NEXT TO THE SCALA TTMPANI. 

a. that end of the lamina spiralis which passes into the inner wall, pillar, or modio- 
lus of the bony cochlea; c, the outer wall of the bony cochlea; Sea. T., the cavity of 
the scala tympani ; Sea.M., the cavity of the scala media ; d, the elastic basilar mem- 
brane which separates the scala media from the scala tympani ; F., a vessel which lies 
in this, cut through ; e, the so-called membrane of Corti ; C C\ the fibres of Corti ; 
VII., the filaments of the auditory nerve. It is doubtful whether the membrane of 
Corti really has the extent and connections given to it in this figure. The membrane 
of Eeissner which separates the scala media from the scala vestibuli is not represented. 
If it were, the letters Sea. V. would be seen to lie in the scala media, and net in the 
scala vestibuli. 



THE MECHANISM OF HEARING. 233 

Rtiss?ier. The opposite or lower wall, which separates it 
from the seala tympani, is the basilar membrane. The 

latter is very elastic, and on it rest the fibres of Corti 
( C\ Fig. 84). each of which is composed of two filaments 
joined at an angle. An immense number of these filaments 
are set side by side, with great regularity, throughout the 
whole length of the seala media, so that this organ pre- 
sents almost the appearance of a key- board, if viewed from 
either the seala vestibuli or the seala tympani. These 
fibres of Corti lie among a number cf epithelium cells 
forming the lining of the seala media at this part, and 
those cells which are close to the fibres of Corti have a 
peculiarly modified form. The ends of the nerves have 
not yet been distinctly traced, but they probably come 
into close relation either with these fibres or with the 
modified epithelium cells lying close to them, which are 
capable of being agitated by the slightest impulse. 

249. The Bony Labyrinth. — These essential parts of 
the organ of hearing are, we have seen, lodged in cham- 
bers of the petrous part of the temporal bone. Thus the 
membranous labyrinth is contained in a bony labyrinth of 
corresponding form, of which that part which lodges the 
sac is termed the vestibule, and those portions which con- 
tain the semicircular canal, the bony semicircular ca?ials. 
And the seala media is contained in a spirally-coiled cham- 
ber, the cochlea, which it divides into two passages. Of 
these, one, the seala vestibuli, is so called because at the 
broad end or base of the cochlea it opens directly by a 
wide aperture into the vestibule; by this opening the 
perilymph which fills the vestibule and bony semicircular 
Canals, and surrounds the membranous labyrinth, is put in 

free communication with the perilymph which fills the seala 

stibuli of the cochlea, and, by means of the communica- 
tion which exists between the two Bcabe ;»t the summit of 

the -pin*, with that of the seala tympani also. 

In the fresh State, this collection of chambers in the 



234 



ELEMENTARY PHYSIOLOGY. 



petrous bone is perfectly closed ; but in the dry skull there 
are two wide openings, termed fenestrce, or windows, on 
its outer wall; i. e., on the side nearest the outside of the 
skull. Of these fenestras, one, termed ovalis (the oval win- 
dow), is situated in the wall of the vestibular cavity; the 
ether, rotunda (the round window), behind and below this, 
is the open end of the scala tympani at the base of the 
spire of the cochlea. In the fresh state, each of these win- 
dows or fenestras is closed by a fibrous membrane, continu- 
ous with the periosteum of the bone. 

Co. 




'je.Mi 



Fig. 85. 

Transverse Section through the Side-Walls of the Skull to show the Parts 

of the Ear. 

Cb., concha or external ear; EM., external auditory meatus; Ty.M.. tympanic 
membrane; Inc., Mall , incus and malleus; J.S.C., P.S.O., E.8.C.. anterior, posterior, 
and external semicircular canals ; Coc, cochlea ; Eu., Eustachian tube; 7.3/.. internal 
auditory meatus, through which the auditory nerve passes to the organ of hearing. 



The fenestra rotunda is closed only by membrane; but 
fastened to the centre of the membrane of the fenestra 
ovalis, so as to leave only a narrow margin, is an oval 
plate of bone, part of one of the little bones to be de- 
scribed shortly. 



! 



THE MECHANISM OF HEARING. 



235 



250. Tympanum and Eustachian Tube. — The outer wall 
of the internal ear is still far away from the exterior of the 
skull. Between it and the visible opening of the ear, in 
fact, are placed in a straight line, first, the drum of the ear, 
or tympanum ,* secondly, the long external passage, or 
meatus (Fig. 85). 

The drum of the ear and the external meatus, which 
together constitute the middle ear, would form one cavity, 
were it not that a delicate membrane, the tympanic mem- 
brane (Ty.JT., Fig. 85), is tightly stretched in an oblique 
direction across the passage, so as to divide the compara- 
tively small cavity of the drum fi om the meatus. 




JitC 



Fig. 96. 



Tut. Membrane of the Dpxm of the Ear seen from the inner Side, with thi 
Bona of the Ear: and the Walls of the Tympanum, with the Air- 
cells' in the Mastoid Part of the Temporal Bone. 

J/.r., mastoid cells : Mall, malleus ; Inc.. incus : St.. stapes : a b. lines drawn through 
the horizontal axis on which the malleus and incus turn . 

The membrane of the tympanum thus prevents any 
communication by means of the meatus, between the drum 
and the external air, but such a communication is pro- 
vided, though in a roundabout way, by the Eustachian 
tube (/,'".. Elg. 85), which leads directly from the fore 
part of the drum inwards to the roof of the pharynx, 
where it opens. 

251. The Auditory Ossicles. — Three small bones, the 



236 



ELEMENTARY PHYSIOLOGY. 



auditory ossicles, lie in the cavity of the tympanum. One 
of these is the stapes, a small bone shaped like a stirrup. 
It is the foot-plate of this bone which, as already men- 
tioned, is firmly fastened to the membrane' of the fenestra 
ovalis, while its hoop projects outwards into the tympanic 
cavity (Fig. 86). 

Another of these bones is the malleus (Mall., Figs. 85, 
86, 87), or hammer-bone, a long process of which is simi- 
larly fastened to the inner side of the tympanic membrane 
(Fig. 87), and a very much smaller process, the slender 
process, is fastened, as is also the body of the malleus, 
to the bony wall of the tympanum by ligaments. The 




Fig. 87. 

A Diagram illustrative of the relative Positions of the various Parts of 

the Ear. 

E.M.* external auditory meatus ; Ty.M.* tympanitic membrane; Ty.* tympanum; 
Mall.* malleus ; Inc.* incus ; Stp.* stapes ; F.o.* fenestra ovalis ; F.r.* fenestra rotunda ; 
Eu.* Eustachian tube ; M.L.* membranous labyrinth, only one semicircular canal with 
its ampulla being represented ; Sea. V.* Sea. T.\ Sca.M.* the scala? of the cochlea, which 
is supposed to be unrolled. 

rounded surface of the head of the malleus fits into a cor- 
responding pit in the end of a third bone, the incus or 
anvil-bone, which has two processes — one, horizontal, which 



THE MECHANISM OF HEARING. 237 

rests upon a support a iron loci to it by the walls of the 
tympanum ; while the other, vertical, descends almost par- 
allel with the long process of the malleus, and articulates 
with the stapes, or rather unites with a little bone, the 
OS orbiculare, which articulates with the stapes (Figs. 86 
and 87). 

The three bones thus form a chain between the fenestra 
ovalis and the tympanic membrane ; and the whole series 
turns upon an horizontal axis, the two ends of which, formed 
by the horizontal process of the incus and the slender pro- 
3S of the malleus, rest in the walls of the tympanum. 
The general direction of this axis is represented by the 
line a b in Fig. 86, or by a line perpendicular to the plane 
oi the paper, passing through the head of the malleus in 
Fig. 87. It follows, therefore, that whatever causes the 
membrane of the drum to vibrate backwards and forwards, 
must force the handle of the malleus to travel in the same 
way. This must cause a corresponding motion of the long 
process of the incus, the end of which must drag the stapes 
backwards and forwards. And, as this is fastened to the 
membrane of the fenestra ovalis, which is in contact with 
the perilymph, it must set this fluid vibrating throughout 
its whole extent, the thrustings in of the membrane of the 
fenestra ovalis being compensated by corresponding thrust- 
ings out of the membrane of the fenestra rotunda, and vice 

The vibrations of the perilymph thus produced will af- 
i < t the endolymph, and this the otolithes, hairs, or fibres; 
by which, finally, the auditory nerves will be excited. 

252. The Muscles of the Tympanum. — The membrane 
of tli'" fenestra ovalis and the tympanic membrane will ne- 

sarily vibrate the more freely the looser they are, and 

the rever-". Hut there are two musclefl — one, called the 

stapedius, which passes from the floor of the tympanum to 

the orbicular bone, and the other, the t< nsor fi/un><i/ii, from 
the front wall of the drum t<» the malleus. Each of the 



238 ELEMENTARY PHYSIOLOGY. 

muscles when it contracts tightens the membranes in ques- 
tion, and restricts their vibrations, or, in other words, tends 
to check the effect of any cause which sets these mem- 
branes vibrating. 

253. The Concha,— The outer extremity of the external 
meatus is surrounded by the concha or external ear (Co., 
Fig. 85), a broad, peculiarly-shaped, and for the most part 
cartilaginous plate, the general plane of which is at right 
angles with that of the axis of the auditory opening. The 
concha can be moved by most animals, and by some human 
beings, in various directions by means of muscles, which 
pass to it from the side of the head. 

Section IV. — Working of the Auditory Mechanism. 

254. Nature of Sound. — The manner in which the com- 
plex apparatus now described intermediates between the 
physical agent, which is the condition of the sensation of 
sound, and the nervous expansion, the affection of which 
alone can excite that sensation, must next be considered. 

All bodies which produce sound are in a state of vibra- 
tion, and thej' communicate the vibrations of their own sub- 
stance to the air with which they are in contact, and thus 
throw that air into waves, just as a stick waved backwards 
and forwards in water throws the water into waves. 

The aerial waves, produced by the vibrations of sono- 
rous bodies, in part enter the external auditory passage, and 
in part strike upon the concha of the external ear and the 
outer surface of the head. It may be that some of the 
latter impulses are transmitted through the solid structure 
of the skull to the organ of hearing ; but before they 
reach it they must, under ordinary circumstances, have be- 
come so scanty and w T eak, that they ma,y be left out of 
consideration. The aerial waves which enter the meatus 
all impinge upon the membrane of the drum and set it 
vibrating, stretched membranes taking up vibrations from 
the air with great readiness. 



WORKING OF THE AUDITORY MECHANISM. 239 

255. Vibrations of the Tympanum. — The vibrations 
thus set up in the membrane of the tympanum are com- 
municated, in part, to the air contained in the drum of the 
ear, and, in part, to the malleus, and thence to the other 
auditory ossicles. 

The vibrations communicated to the air of the drum 
impinge upon the inner wall of the tympanum, on the 
greater part of which, from its density, they can produce 
verv little effect. Where this wall is formed by the mem- 
brane of Ihe fenestra rotunda, however, the communication 
o( motion must necessarily be greater. 

The vibrations which are communicated to the malleus 
and the chain of ossicles may be of two kinds: vibrations 
of the particles of the bones, and vibrations of the bones 
a- a whole. If a beam of wood, freely suspended, be very 
gently scratched with a pin, its* particles will be thrown 
into a state of vibration, as will be evidenced by the sound 
given out, but the beam itself will not be moved. Again, 
if a strong wind blow against the beam, it will swing visi- 
bly, without any vibrations of its particles among them- 
>elves. On the other hand, if the beam be sharply struck 
with a hammer, it will not only give out a sound, showing 
that its particles are vibrating, but it will also swing from 
the impulse given to its whole mass. 

Under the last mentioned circumstances, a blind man 
standing near the beam would be conscious of nothing but 
the sound, the product of molecular vibration, or invisible 
oscillation of the particles of the beam ; while a deaf man, 
in the same position, would be aware of nothing but the 

ible oscillation of the beam as a whole. 

256. Their Transmission. — Thus, to return to the chain 
of auditory ossicles, while it seems hardly to be doubted 
that, when the membrane of the drum vibrates, they may 
be set vibrating both as a whole and in their particles, it 
depends upon subsidiary arrangements whether the large 
vibrations, or the minute ones, shall make themselves ob- 



240 ELEMENTARY PHYSIOLOGY. 

vious to the auditory nerve, which is in the position of our 
deaf, or blind man. 

The evidence at present is in favor of the conclusion, 
that it is the vibrations of the bones, as a whole, which 
are the chief agents in transmitting the impulses of the 
aerial waves. 

For, in the first place, the disposition of the bones and 
the mode of their articulation are very much against the 
transmission of molecular vibrations through their sub- 
stance, while, on the other hand, they are extremely favor- 
able to their vibration en masse. The long processes of 
the malleus and incus swing, like a pendulum, upon the 
axis furnished by the short processes of these bones ; while 
the mode of connection of the incus with the stapes, and 
of the latter with the edges of the fenestra ovalis, allows 
that bone free play, inwards and outwards. In the second 
place the total length of the chain of ossicles is very small 
compared with the length of the waves of audible sounds, 
and physical considerations teach us that in a like small 
rod, similarly capable of swinging en masse, the minute 
molecular vibrations w^ould be inappreciable. Thirdly, it 
is affirmed, as the result of experiments, that the bone 
called columella, which, in birds, takes the place of the 
chain of ossicles in man, does actually vibrate as a whole, 
and at the same rate as the membrane of the drum, when 
aerial vibrations strike upon the latter. 

257. The Action of the Auditory Muscles, — Thus, there 
is reason to believe that w^hen the tympanic membrane is 
set vibrating, it causes the process of the malleus, which 
is fixed to it, to swing at the same rate ; the head of the 
malleus consequently turns through a small arc on its 
pivot, the slender process. But the turning of the head 
of the malleus involves that of the head of the incus upon 
its pivot, the short process. In consequence, the long pro- 
cess of the incus swings through an arc which has been 
estimated as being equal to about two-thirds of that de- 



WORKING OF THE AUDITORY MECHANISM. 241 

scribed by the handle of the malleus. The extent of the 
push is thereby somewhat diminished, but the force of the 
push is proportionately increased ; in so confined a space 
this change is advantageous. The long process, however, 
is so fixed to the stapes that it cannot vibrate without, to 
a corresponding extent and at the same rate, pulling this 
out of, and pushing it into, the fenestra ovalis. But every 
pull and push imparts a corresponding set of shakes to the 
perilymph, which fills the bony labyrinth and cochlea, ex- 
ternal to the membranous labyrinth and scala media. These 
shakes are communicated to the endolymph and fluid of 
the scala media, and, by the help of the otolithes and the 
fibres of Corti, are finally converted into impulses, which 
act as irritants of the ends of the vestibular and cochlear 
divisions of the auditory nerve. 

258. Intensity and Quality of Sounds— how discrimi- 
nated. — The difference between the functions of the mem- 
branous labyrinth (to which the vestibular nerve is dis- 
tributed) and those of the cochlea are not quite certainlj r 
made out, but the following views have been suggested : 

The membranous labyrinth may be regarded as an ap- 
paratus whereby sounds are appreciated and distinguished 
according to their intensity or quantity ; but which does 
not afford any means of discriminating their qualities. 
The vestibular nerve tells us that sounds are weak or 
loud, but gives us no impression of tone, or melody, or 
harmony. 

The cochlea, on the other hand, it is supposed, enables 
the mind to discriminate the quality rather than the quan- 
tity or intensity of sound. It is suggested that the excite- 
ment of any single filament of the cochlear nerve gives 
rise, in the mind, to a distinct musical impression ; and 
that every fraction of a tone which a well-trained ear is 
capable of distinguishing is represented by its separate 
nerve-fibre. Under this view the scala media resembles a 
key-board, in function, as well as in appearance, the fibres 
16 



242 ELEMENTARY PHYSIOLOGY. 

of Corti being the keys, and the ends of the nerves repre- 
senting the strings which the keys strike. If it were pos- 
sible to irritate each of these nerve-fibres experimentally, 
we should be able to produce any musical tone, at will, in 
the sensorium of the person experimented upon, just as 
any note on a piano is produced by striking the appro- 
priate key. 

259. Probable Function of the Fibres of Corti. — A 
tuning-fork may be set vibrating, if its own particular 
note, or one harmonic with it, be sounded in its neighbor- 
hood. In other words, it will vibrate under the influence 
of a particular set of vibrations, and no others. If the 
vibrating ends of the tuning-fork were so arranged as to 
impinge upon a nerve, their repeated minute blows would 
at once excite this nerve. 

Suppose that of a set of tuning-forks, tuned to every 
note and distinguishing fractions of a note in the scale, one 
were thus connected with the end of every fibre of the 
cochlear nerve ; then any vibration communicated to the 
perilymph would affect the tuning-fork which could vibrate 
with it, while the rest would be absolutely, or relatively, 
indifferent to that vibration. In other words, the vibration 
would give rise to the sensation of one particular tone, and 
no other, and every musical interval would be represented 
by a distinct impression on the sensorium. 

It is suggested that the fibres of Corti are competent 
to perform the function of such tuning-forks ; that each of 
them is set vibrating to its full strength by a particular 
kind of wave sent through the perilymph, and by no other; 
and that each affects a particular fibre of the cochlear 
nerve only. But it must be remembered that the view 
here given is a suggestion only which, however probable, 
has not yet been proved. Indeed, recent inquiries have 
rather diminished than increased its probability. 

The fibres of the cochlear nerve may be excited by in- 
ternal causes, such as the varying pressure of the blood 



STRUCTURE AND ACTION OF THE RETINA. 243 

and the like : and in some persons such internal influences 
do give rise to veritable musical spectra, sometimes of a 
very intense character. But, for the appreciation of music 
produced external to us, we depend upon the intermedia- 
tion of the scala media and its Cortian fibres. 

260. Function of the Tympanic Muscles and Eustachian 
Tube. — It has already been explained that the stapedius 
and tensor tympani muscles are competent to tighten the 
membrane of the fenestra ova] is and that of the tym- 
panum, and it is probable that they come into action 
when the sonorous impulses are too violent, and would 
produce too extensive vibrations of these membranes. 
They therefore tend to moderate the effect of intense 
sound, in much the same way that, as we shall find, the 
contraction of the circular fibres of the iris tends to mod- 
erate the effect of intense light in the eye. 

The function of the Eustachian tube is, probably, to 
keep the air in the tympanum, or on the inner side of the 
tympanic membrane, of about the same tension as that on 
the outer side, which could not always be the case if the 
tympanum were a closed cavity. 



CHAPTER IX. 

THE O B G A N OF SIGHT. 

Ti'>\ I. — Structure and Action oftfu Retina, 

261. General Structure of the Eye. — [n studying the 
of the sense of Bight, the eye, it is needful to be- 
come acquainted, firstly, with the structure and properties 
of tic aion in which the optic nerve,or nerve 

ght, terminal ith the physical agent of 

: - lion; thirdly, with the intermediate apparatus by 



244 ELEMENTARY PHYSIOLOGY. 

which the physical agent is assisted in acting upon the 
nervous expansion. 

The ball, or globe, of the eye is a globular body, mov- 
ing freely in a chamber, the orbit, which is furnished to it 
by the skull The optic nerve, the root of which is in the 
brain, leaves the skull by a hole at the back of the orbit, 
and enters the back of the globe of the eye, not in the 
middle, but on the inner, or nasal, side of the centre. 
Having pierced the wall of the globe, it spreads out into 
a very delicate membrane, varying in thickness from -^th 
of an inch to less than half that amount, which lines the 
hinder two-thirds of the globe, and is termed the retina. 
This retina is the only organ connected with sensory ner- 
vous fibres which can be affected, by any agent, in such a 
manner as to give rise to the sensation of light. 

262. The Surface of the Retina. — If the globe of the 
eye be cut in two, transversely, so as to divide it into an 
anterior and a posterior half, the retina will be seen lining 
the whole of the concave wall of the posterior half as a 
membrane of great delicacy, and, for the most part, of even 
texture and smooth surface. But, exactly opposite the 
middle of the posterior wall, it presents a slight circular 
depression of a yellowish hue, the macula lutea, or yellow 
spot (Fig. 90, m.l. / Fig. 94, 8") — not easily seen, however, 
unless the eye be perfectly fresh — and, at some distance 
from this, towards the inner, or nasal, side of the ball is 
a radiating appearance, produced by the entrance of the 
optic nerve and the spreading out of its fibres into the 
retina. 

263. Microscopic Structure of the Eetina.— A very thin 
vertical slice of the retina, in any region except the yellow 
spot, and the entrance of the optic nerve, may be resolved 
into the structures represented separately in Figs. 88, 89. 
The one of these (Fig. 88) occupies the whole thickness of 
the section, and comprises its essential, or nervous ele- 
ments. The outer (or posterior) fourth, or rather less, of 









STRUCTURE AND ACTION' OF THE RETINA. 



245 



the thickness of these consists of a vast multitude of mi- 
nute, either rod-like or conical, bodies, ranged side by side, 
perpendicularly to the plane of the retina. This is the 
layer of rods and cones {be). From the front ends or 

bases of the rods and cones very delicate fibres pass, and 
in each is developed a granule-like body (/> c ), which 






i' 








- 



— 






-\d 








T:n: NSBVOTTS (Fill. BSfc wn TBI CO HIfdT 

- 

: </ </ . inr. r 

r '. pro 
a, which 
. _' ! i « • 1 1 i - • corpuscles, 
nerve. 
I 

. nuclei : '/ / 
• • | 



246 ELEMENTARY PHYSIOLOGY 

forms a part of what has been termed the outer layer of 
granules. It is probable that these fibres next pass into 
and indeed form the close meshwork of very delicate ner- 
vous fibres which is seen at d d' (Fig. 88). From the an- 
terior surface of this meshwork other fibres proceed, con- 
taining a second set of granules, which forms the inner 
granular layer (ff). In front of this layer is a stratum 
of convoluted fine nervous fibres (g </'), and anterior to this 




Fig. 90. 

The Eyeball divided transversely in the Middle Line, and viewed from 

the Front 

«., sclerotic; eh., choroid, seen in section only. r., the cut edge of the retina ; r.r., 
vessels of the retina, springing from o., the optic nerve or blind spot, m.L, the yellow 
spot, the darker spot in its middle being the fovea centralis. 

again numerous ganglionic corpuscles (h h'). Processes 
of these ganglionic corpuscles extend, on the one hand, 
into the layer of convoluted nerve-fibres ; and, on the other, 
are probably continuous with the stratum of fibres of the 
optic nerve (£). 

These delicate nervous structures are supported by a 
sort of framework of connective tissue of a peculiar kind 
(Fig. 89), which extends from an inner or anterior limit- 
ing membrane (£), which bounds the retina and is in con- 
tact with the vitreous humor, to an outer or posterior Urn- 






STRUCTURE AND ACTION OF THE RETINA. o 4 ; 

7 men brane^ which lit^s at t ho anterior ends, or bases, 
of the rods and cones near the level of V c' in Fig, 88. 
Thus the framework is thinner than the nervous substance 

of the retina, and the rods and cones lie altogether outside 
of it, and wholly unsupported by any connective 1 tissue. 
They are, however, as we shall see, embedded in the layer 

of pigment on which the retina rests ("ill). 

The fibres of the optic nerve spread out between the 
limiting membrane (/) and the ganglionic corpuscles (A'), 
and the vessels which enter along with the optic nerve 
ramify between the limiting membrane and the inner gran- 
ules (ff). Thus, not only the nervous fibres, but the 
vest els, are placed altogether in front of the rods and cones. 

At the entrance of the optic nerve itself, the nervous 
fibres predominate, and the rods and cones are absent. In 
the yellow spot, on the contrary, the cones are abundant 
and close set, becoming at the same time longer and more 
slender, while rods are scanty, and are found only towards 
its margin. The layer of fibres of the optic nerve disaj>- 
pears, and all the other layers, except that of the cones, 
become extremely thin in the centre of the macula lutea 
(Fig. 91). 

264. The Sensation of Light. — The most notable prop- 
erty of the retina is its power of converting the vibrations 
of ether, which constitute the physical basis of light, into 
stimulus to the fibres of the optic nerve — which fibres, 
when excited, have the power of awakening i lie sensation 
of light in, or by means of, the brain. The sensation of 
light, it must be understood, is the work of the brain, noi 

the retina: for, if an eve be destroyed, pinching, gal- 
vanizing, or otherwise irritating the optic nerve, will still 

ite the sensation of light, because it throws the fibres 
of the optic nerve into activity; and their activity, how- 
ever produced, brings about in the brain certain changes 
which give rise to the sensation of light. 

Light, falling directly on the optic nerve, does not ex- 



248 



ELEMENTARY PHYSIOLOGY. 



cite it; the fibres of the optic nerve, in themselves, are as 
blind as any other part of the body. But just as the deli- 
cate filaments of the ampulla*, or the otoconia of the ves- 
tibular sac, or the Cortian fibres of the cochlea, are con- 
trivances for converting the delicate vibrations of the 




A Diagrammatic Section of the Macula Lutea, or Yellow Spot. 

(Magnified about sixty diameters.) 

a a, the pigment of the choroid ; b c, rods and cones ; d d, outer granular laver ; 
//, inner granular layer ; g g, molecular layer; hh, ayer of ganglionic cells ; ii, fibres 
of the optic nerve. 






STRUCTURE AND ACTION' OF THE RETINA. 249 

perilymph and endolymph into impulses which ('an excite 
the auditory nerves, so the structures in the retina appear 
to be adapted to c nivert the infinitely more delicate pulses 
of the luminiferous ether into stimuli of the fibres of the 
optic nerve. 

265. The "Blind Spot"— The sensibility of the different 
parts of the retina to light varies very greatly. The point 
of entrance o( the optic nerve is absolutely blind, as may 
be proved by a very simple experiment. Close the left 
eye, and look steadily with the right at the cross on the 
page, held at ten or twelve inches' distance : 



The black dot will be seen quite plainly, as well as the 
cross. Now, move the book slowly towards the eye, which 
must be kept steadily fixed upon the cross ; at a certain 
point the dot will disappear, but, as the book is brought 
still closer, it will come into view again. It results from 
optical principles that, in the first position of the book, 
the figure of the dot falls between that of the cross (which 
throughout lies upon the yellow spot) and the entrance of 
the optic nerve : while in the second position, it falls on 
the entrance of the optic nerve itself; and, in the thin , 
inside that point. So long as the image of the spot 
rests upon the entrance of the optic nerve it is not per- 
ceived, and hence this region of the retina is called the 
blind spot. 

266. Duration of Luminous Impressions. — The impres- 
sion made by light upon the retina not only remains during 
the whole period of the direct action of the light, but baa a 
certain duration of its own, however shorl the time during 

which the light itself lasts. A flash of lightning i-. prac- 
tically, instantaneous, but the sensation of light produced 
by thai flash endure- for an appreciable period It is 

found, in fact, that a luminous impression lastfl for about 

one-eighth of a second ; whence it follow- that, if any two 



250 



ELEMENTARY PHYSIOLOGY. 



luminous impressions are separated by a less interval, they 
are not distinguished from one another. 

For this reason a " Catherine-wheel," or a lighted stick 
turned round very rapidly by the hand, appears as a circle 
of fire ; and the spokes of a coach-wheel at speed are not 
separately visible, but only appear as a sort of opacity, or 
film, within the tire of the wheel. 







; j coc 



Fig. 92. 



Fig. 93. 



Pigment-Cells from the Choroid Coat. 

Fig 92.— Branched pigment -cells from the deep layer. 
Fig. 93.— Pigment epithelium, a, seen in face; b, seen in profile; c, pigment 
granules. 



267. Exhaustion of the Retina, — The excitability of the 
retina is readily exhausted. Thus, looking at a bright 
light rapidly renders the part of the retina on which the 
light falls, insensible ; and, on looking from the bright light 
towards a moderately-lighted surface, a dark spot, arising 
from a temporary blindness of the retina in this part, ap- 
pears in the field of view. If the bright light be of one 
color, the part of the retina on which it falls becomes in- 
sensible to rays of that color, but not to the other rays of 
the spectrum. This is the explanation of the appearance 
of what are called complementary colors. For example, if 
a bright-red wafer be stuck upon a sheet of white paper, 
and steadily looked at for some time with one eye, when 
the eye is turned aside to the white paper a greenish spot 



STRrCTTRE AND ACTK)N OF THE RETINA. 251 

will appear, of about the size and shape of the wafer. The 
red image has, in fact, fatigued the part of the retina on 
which it fell for red light, but has left it sensitive to the 
remaining colored rays of which white light is composed. 
But we know that, if from the variously colored rays which 
make up the spectrum of white light we take away all 
the red rays, the remaining rays together make up a sort 
of green. So that, when white light falls upon this part, 
the red rays in the white light having no effect, the result 
of the operation of the others is a greenish hue. If the 
wafer be green, the complementary image, as it is called, 
is red. 

268. Color-Blindness. — In some persons, the retina ap- 
pears to be affected in one and the same way by rays of 
light of various colors, or even of all colors. Such color- 
Wind persons are unable to distinguish between the leaves 
of a cherry-tree and its fruit br the color of the two, and 
see no difference between blue and yellow cloth. 

This peculiarity is simply unfortunate for most people, 
hut it may be dangerous if unknowingly possessed by rail- 
way guards or sailors. It probably arises either from a 
defect in the retina, which renders that organ unable to 
respond to different kinds of luminous vibrations, and con- 
sequently insensible to red rays or yellow rays, etc., as the 
may be, or it may proceed from some unusual absorp- 
tive power of the humors of the eye w T hich prevents par- 
ticular rays from reaching the retina ; or the fault may lie 
in the brain itself. 

269. Luminous Effects of Pressure on the Eye. — The 
sensation of light may be excited by other causes than the 
impact of the vibrations of the iuminiferous ether upon the 
retina. Thus, an electric shock sent through the eve, <ri V es 
rise to the appearance of a flash of lighl : and pressure on 
any pari of tii<- retina produces a luminous image, which 

long a- the pressure, and is called a phoaphene. 
If the point of the finger be pressed upon the cuter side of 



252 ELEMENTARY PHYSIOLOGY. 

the ball of the eye, the eyes being shut, a luminous image 
— which, in my own case, is dark in the centre, with a 
bright ring at the circumference (or, as Newton described 
it, like the u eye " in a peacock's tail) — is seen ; and this 
image lasts as long as the pressure is continued. Most 
persons, again, have experienced the remarkable display 
of subjective fireworks which follows a heavy blow upon 
the eyes, produced by a fall from a horse, or by other 
methods well known to English youth. 

It is doubtful, however, whether these effects of press- 
ure, or shock, really arise from the excitation of the retina 
proper, or whether they are not rather the result of the 
violence done to the fibres of the optic nerve apart from 
the retina. 

270. Function of the Rods and Cones. — The last para- 
graph raises a distinction between the " fibres of the optic 
nerve " and the " retina " which may not have been antici- 
pated, but which is of much importance. 

We have seen that the fibres of the optic nerve ramify 
in the inner or anterior fourth of the thickness of the 
retina, while the layer of rods and cones forms its outer 
or posterior fourth. The light, therefore, must fall first 
upon the fibres of the optic nerve, and, only after travers- 
ing them, can it reach the rods and cones. Consequently, 
if the fibrillas of the optic nerve themselves are capable of 
being affected by light, the rods and cones can only be 
some sort of supplementary optical apparatus. But, in 
fact, it is the rods and cones which are affected by light, 
while the fibres of the optic nerve are themselves insensi- 
ble to it. The evidence on which this statement rests is — 

a. The blind spot is full of nervous fibres, but has no 
cones or rods. 

b. The yellow spot, wmere the most acute vision is 
situated, is full of close-set cones, but has no nerve-fibres. 

c. If you go into a dark room with a single small bright 
candle, and, looking towards a dark wall, move the light up 



STRUCTURE AND ACTION OF THE RETINA. 253 

and down, close to the outer side of one eye, so as to allow 
the light to tall very obliquely into the eye, one of what are 
called Purkinje's figures is seen. This is a vision of a series 

diverging, branched, red lines on a dark field, and in 
the interspace of two of these Lines b a s> it of cup-shaped 
disk. The red lines are the retinal blood-vessels, and the 
disk is the yellow spot As the candle is moved up and 
down, the red lines shift their position, as shadows do 
when the light which throws them changes its pla 

Now, as the light falls on the inner face of the retina, 
and the images of the ves<el< to which it gives rise shift 
their position as it moves, whatever perceives these images 
must needs lie on the other, or onter, side of the vessels. 
But the fibres of the optic nerve lie among the vessels, and 
the only retinal structures which lie outside them are the 
granular layers and the rods and cones. 

'/. Just a-, in the skin, there is a limit of distance 
within which two points give only one impression, bo 
there is a minimum distance by which two points of light 
falling on the retina must be separated in order to appear 
- two. And this distance corresponds pretty well with 
the diameter of the cones. 

Thus it would appear that these remarkable structures, 

upon the outer surface- of the retina, are like so many 
Bnger-points, endowed with a touch delicate enough to feel 
the luminous vibrati 

271. Formation of Visual Ideas — We, however, are not 

Only conscious of the general sensation of light, we can 
not only appreciate the quantity and color of tin 1 light 
admitted into the eye, the rods and cones (»f <>nr retina 

ble of converting luminous vibrations 
into stimuli of the optic nerve, but they can do this in 

such :i way that different objects in the external world 
a • t<> different and distinct pi in the sensory 

nerve and the parts of the brain with which it is con- 
different and distinct ideas, For 



254 ELEMENTARY PHYSIOLOGY. 

instance, the light coming from a tree not only causes 
luminous sensations of a certain intensity and of certain 
shades of color, but makes such an impression on our 
brain as to give rise to the idea of a tree. In other words, 
we possess the power of distinct vision of objects which 
are conceived as external. 

Now, one of the conditions of distinct vision is, that a 
sharp, well-defined image of the thing to be seen should 
be thrown upon the retina, and a great deal of the inter- 
mediate apparatus of the eye is concerned with the pro- 
duction of this well-defined image. We often speak of 
the ideas caused by external objects as images ; but it will 
of course be remembered that the image on the retina, 
which is a mere physical thing, is altogether different from 
that mental image which arises in consequence of changes 
which the affection of the retina causes in the brain, and 
which is an idea. 

Section II. — The Luminous Agent. 

272. The Convex Lens. — The physical agent which 
gives rise to vision is light, which is now conceived to be 
a very attenuated fluid, the ether, vibrating in a particular 
way. The properties of this physical agent, and the prin- 
ciples of optics, must be studied elsewhere. At present it 
is only necessary to advert to some facts, of which every 
one can assure himself by simple experiments. An ordi- 
nary spectacle-glass is a transparent body denser than the 
air, and convex on both sides. If this lens be held at a 
certain distance from a screen or wall in a dark room, and 
a lighted candle be placed on the opposite side of it, it 
w 7 ill be easy to adjust the distances of candle, lens, and 
wall, so that an image of the flame of the candle, upside 
down, shall be thrown upon the wall. 

273, Formation of the Luminous Picture. — The spot on 
which the image is formed is called & focus. If the candle 
be now brought nearer to the lens, the image on the wall 



THE LUMINOUS AGENT. 255 

will enlarge, and grow blurred and dim, but may be re- 
stored to brightness and definition by moving the lens far- 
ther Brora the wall. But, if, when the new adjustment has 
taken place, the candle be moved away from the Ions, the 
image will again become confused, and, to restore its 
clearness, the Ions will have to be broughl Dearer the wall. 

Thus a convex Ions forms a distinct picture of luminous 
objects, but only at the focus on the side of the Ions oppo- 
site to the object; and that focus is nearer when the 
object is distant, and farther off when it is near. 

274. Effect of varying the Convexity. — Suppose, how- 
ever, that, leaving* the candle unmoved, a Ions with more 
convex surfaces is substituted for the first, the image will 
be blurred, and the lens will have to be moved nearer the 
wall to give it definition. If, on the other hand, a lens 
with less convex surfaces is substituted for the first, it 
must be moved farther from the wall to attain the same 
end. 

In other words, other things being alike, the more con- 
vex the lens, the nearer its focus ; the less convex, the 
farther off its focus. 

ft the lens were clastic, pulling ii at the circumference 
would render it flatter, and thereby lengthen its focus; 
while, when let go again, it would become more convex, 
and of shorter focus. 

Any materia] more refractive than the medium in which 

it i< placed, if ij have a convex -in'face. causes the rays of 

light which pass through the less refractive medium to 
that surfe inverse towards a focus. If a watch-glass 

be fitted into one side of a box, and. the box be then filled 
water, a candle may be placed at such a distance out- 
side tip* watch-glass that an image of its Same shall fall 
on the opposite wall of the box. If, under these circum- 
stances, a doubly OOnvei lens of glass were introduced into 
the water in the path of tin rays, it would act (though less 

■rfully than if it were in air! in bringing the ravs more 



256 ELEMENTARY PHYSIOLOGY. 

quickly to a focus, because glass refracts light more strongly 
than water does. 

A camera-obscura is a box, into one side of which a 
lens is fitted, so as to be able to slide backwards and for- 
wards, and thus throw on the screen at the back of the box 
distinct images of bodies at various distances off. Hence 
the arrangement just described might be termed a water 
camera. 

Section III. — The Intermediate Apparatus. 

275. The Visual Mechanism. — The intermediate organs, 
by means of which the physical agent of vision, light, is 
enabled to act upon the expansion of the optic nerve, com- 
prise three kinds of apparatus : (a) a " water camera," the 
eyeball ; (b) muscles for moving the eyeball ; (c) organs 
for protecting the eyeball, viz., the eyelids, with their 
lashes, glands, and muscles ; the conjunctiva ; and the 
lachrymal gland and its ducts. 

The eyeball is composed, in the first place, of a tough, 
firm, spheroidal case consisting of fibrous or connective 
tissue, the greater part of which is white and opaque, and 
is called the sclerotic (Fig. 94, 2). In front, however, this 
fibrous capsule of the eye, though it does not change its 
essential character, becomes transparent, and receives the 
name of the cornea (Fig. 94, 1). The corneal portion of 
the case of the eyeball is more convex than the sclerotic 
portion, so that the whole form of the ball is such as would 
be produced by cutting off a segment from the front of a 
spheroid of the diameter of the sclerotic, and replacing this 
by a segment cut from a smaller, and consequently more 
convex, spheroid. 

276. The Humors and Crystalline Lens, — The corneo- 
sclerotic case of the eye is kept in shape by what are 
termed the humors — watery or semi-fluid substances, one 
of which, the aqueous humor (Fig. 94, 7'), which is hardly 
more than water holding a few organic and saline sub- 






Till; INTERMEDIATE APPARATUS. 



257 



stances in solution, distends the corneal chamber of the 
eve, while the other, the vitreous (Fig. 94, 13), which is 
rather a delicate jelly than a regular fluid, keeps the scle- 
rotic chamber full. 

The two humors are separated by the very beautiful, 
transparent, doubly-convex crystalline lens (Fig. 9-4, 12) 3 
denser, and capable of refracting light more strongly than 
either of the humors. The crystalline lens is composed 
of fibres having a somewhat complex arrangement, and is 
highly elastic. It is more convex behind than in front, 




Fig. 04. 

IIORTZONTU. SlXTION OF TJ1E EYEBALL. 

1. cornea: I', conjunctiva: 2. sclerotic^ -. -heath of optic ncrvo : 3. choroid; 8", 

>f the retina; 4. ciliary muscle; r. circular portion of ciliary muscle : 

.'.ciliary process; S, posterior chamber between 7. th«- Iris, and the suspensory Hgs> 

t; T', anterior chamber ; 8L artery of retina bo theoentre of the optic nerve: 3', 

tie of blind spot; v \ macula latea ; 9, on semta(thie le of course ooi seen in I 

itroduced to show its position) ; LQ, space' behind the bus- 

12, crystalline lens ; 18, vitreous humor; 14 marks 

the position of the c liary ligament : n d the sctual sye of which this is 

■a enact copy, thi opened, curiously. eno u ghs n«<t t«> }><• in the optflc axis) ^ 

B\ lirif of pquatot ■ .11 

17 



256 ELEMENTARY PHYSIOLOGY. 

and it is kept in place by a delicate, but at the same time 
strong and elastic, membranous frame or suspensory liga- 
ment, which extends from the edges of the lens to what 
are termed the ciliary processes of the choroid coat (Figs. 
94, 5, and 95, c). In the ordinary condition of the eye 
this ligament is kept tense, i. e., is stretched pretty tight, 
and the front part of the lens is consequently flattened 
against it. 

277. The Choroid and Ciliary Processes. — This choroid 
coat (Fig. 94, 3) is a highly- vascular membrane, in close con- 
tact with the sclerotic externally, and lined, internally, by a 
layer of small polygonal bodies containing much pigmentary 
matter, called pigment-cells (Figs. 92, 93). These pigment- 
cells are separated from the vitreous humor by the retina 
only. The rods and cones of the latter are in immediate 
contact with them. The choroid lines every part of the 
sclerotic, except just where the optic nerve enters it at a 
point below, and to the inner side of the centre of the 
back of the eye ; but, when it reaches the front part of the 
sclerotic, its inner surface becomes raised up into a number 
cf longitudinal ridges, with intervening depressions, like 
the crimped frills of a lady's dress, terminating within and 
in front by rounded ends, but passing, externally, into the 
iris. These ridges, which when viewed from behind seem 
to radiate on all sides from the lens (Figs. 95, c, and 94, 5), 
are the above-mentioned ciliary processes. 

278. The Iris and Ciliary Muscle. — The iris itself 
(Figs. 94, 7, and 95, a, b) is, as has been already said, a 
curtain with a round hole in the middle, provided with cir- 
cular and radiating unstriped muscular fibres, and capable 
of having its central aperture enlarged or diminished by the 
action of these fibres, the contraction of which, unlike that 
of other unstriped muscular fibres, is extremely rapid. The 
edges of the iris are firmly connected with the capsule of 
the eye, at the junction of the cornea and sclerotic, by the 
connective tissue which enters into the composition of the 



THE INTERMEDIATE APPARATUS. 259 

so-called ciliary ligament. Unstriped muscular fibres, 
having the same attachment in front, spread backwards on 
to the outer surface of the choroid, constituting the ciliary 
muscle (Fig. 04, 4). If these fibres contract, ii is obvious 

that they will pull the choroid forward ; and as the frame, 
0>r suspensory ligament of the lens, is connected with the 




Fig. 05. 

View OF Front Half of Eyeball seen from behind. 

a. cirr-ular fibres; h. radiating fibres of the iris: c, ciliary processes; d, choroid. The 
crystalline lens has been removed. 



ciliary processes (which simply form the anterior termina 
tion of the choroid), this pulling forward of the choroid 
comes to the same thing as a relaxation of the tension of 
that suspensory ligament, which, as I have just said, like 
the lens itself, is highly elastic. 

The iris doe- not haug down perpendicularly into the 
ice between the front face of the crystalline lens and 
the posterior surface of the cornea, which is filled by the 
aqueous humor, hut applies itself very closely to tie an- 
terior face of the lens, so that hardly any interval is left 
1).-; wo. n the two ( Pigs. 9 1 and 96). 

279. Position of the Retina. — The retina, ;i- we have 

n, lines the interior of the eye, being placed between 

the choroid nnd vitreous humor, it- rods and cones being 



260 ELEMENTARY PHYSIOLOGY. 

embedded in the former, and its anterior limiting mem- 
brane touching the latter. 

About a third of the distance back from the front of the 
eye the retina seems to end in a wavy border called the 
or a serrata (Fig. 94, 9), and in reality the nervous ele- 
ments of the retina do end here, having become consider- 
ably reduced before this line is reached. Some of the 
connective-tissue elements, however, pass on as a delicate 
kind of membrane at the back of the ciliary processes 
towards the crystalline lens. 

Section IV. — Focal Adjustment. 

280. The Iris a Self-regulating Diaphragm.— The eye- 
ball, the most important constituents of which have now 
been described, is, in principle, a camera of the kind de- 
scribed above — a water camera. That is to say, the scle- 
rotic answers to the box, the cornea to the watch-glass, the 
aqueous and vitreous humors to the water filling the box, 
the crystalline to the glass lens, the introduction of which 
was imagined. The back of the box corresponds with the 
retina. 

But further, in an ordinary camera obscura, it is found 
desirable to have what is termed a diaphragm (that is, an 
opaque plate with a hole in its centre) in the path of the 
rays, for the purpose of moderating the light and cutting 
off the marginal rays which, owing to certain optical prop- 
erties of spheroidal surfaces, give rise to defects in the 
image formed at the focus. 

In the eye, the place of this diaphragm is taken by the 
iris, which has the peculiar advantage of being self-regu- 
lating : dilating its aperture, and admitting more light 
when the light is w^eak ; but contracting its aperture and 
admitting less light when the illumination is strong. 

281. Necessity of Adjustment. — In the water camera, 
constructed according to the description given above, there 
is the defect that no provision exists for adjusting the 






FOCAL ADJUSTMENT. 201 

focus to the varying distances of objects. If the box were 

so made that its back, on which the image is supposed to 
he thrown, received distinct images of very distant ob- 
jects, all near ones would be indistinct. And if, on the 
other hand, it were lit ted to receive the image of near 
objects, at a given distance, those of either nearer, or more 
distant, bodies would be blurred and indistinct. In the 
ordinary camera this difficulty is overcome by sliding the 
lenses in and out, a process which is not compatible with 
the construction of our water camera. But there is clearly 
oik way, among many, in which this adjustment might be 
effected — namely, by changing the glass lens ; putting in 
a less convex one when more distant objects had to be 
pictured, and a more convex one when the images of 
nearer objects were to be thrown upon the back of the 
box. 

But it would come to the same thing, and be much 
more convenient, if, without changing the lens, one and 
tin 1 same lens could be made to alter its convexity. This 
i> what actually is done in the adjustment of the eye to 
distances. 

282. Experiment— Adjustment requires Effort. — The 
simplest way of experimenting on the adjustment of the 
' //' is to stick two stout needles upright into a straight 
piece of wood, not exactly, but nearly in the same straight 
line, so that, on applying the eye to one end of the piece 
of wood, oik* needle (") shall be seen about six inches off, 
and the Other (ft) just on one side of it at twelve inches' 
distance. 

If the observer look at the needle ft, he will find that 

he 5 'TV distinctly, and without the least sense of 

effort; but the image of <i \> blurred and more or less 
double. Now lei him try to make this blurred imago of 
the needle a distinct. He will find he ran do bo readily 
enough, but that the act is accompanied by ;t sense of 
ft Bomewh< re in the eye. And, in proportion as a 



262 



ELEMENTARY PHYSIOLOGY. 



becomes distinct, b will become blurred. Nor will any 
effort enable him to see a and b distinctly at the same 
time. 

283. The Mechanism of Adjustment explained.— Multi- 
tudes of explanations have been given of this remarkable 
power of adjustment, but it is only within the last few 
years that the problem has been solved, by the accurate 
determination of the nature of the changes in the eye 
which accompany the act. When the flame of a taper is 
held near, and a little on one side of, a person's eye, any 
one, looking into the eye from a proper point of view, will 
see three images of the flame, two upright and one in- 
verted. One upright figure is reflected from the front of 




Fig. 96. 

Illustrates the change in the form of the lens when adjusted — A to distant, B to near 

objects. 



the cornea, which acts as a convex mirror. The second 
proceeds from the front of the crystalline lens, which has 
the same effect ; while the inverted image proceeds from 
the posterior face of the lens, which, being convex back- 
wards, is, of course, concave forwards, and acts as a con- 
cave mirror. 

Suppose the eye to be steadily fixed on a distant ob- 
ject, and then adjusted to a near one in the same line of 
vision, the position of the eyeball remaining unchanged. 
Then the upright image reflected from the surface of the 
cornea, and the inverted image from the back of the lens, 
will remain unchanged, though it is demonstrable that 
their size or apparent position must change if either the 



FOCAL ADJUSTMENT. 263 

cornea, or the back of the lens, alter either their form or 
their position. But the second upright image, that re- 
flected by the front face of the lens, does change both its 
size and its position; it comes forward and grows smaller, 
proving that the front face of the lens has become more 
convex. The change of form of the lens is, in fact, that 
represented in Fig. 9b. 

These may be regarded as the facts of adjustment, with 
which all explanations of that process must accord. They 
at once exclude the hypotheses (1) that adjustment is the 
result of the compression of the ball of the eye by its mus- 
cles, which would cause a change in the form of the cornea ; 
(*2) that adjustment results from a shifting of the lens 
bodily, for its hinder face does not move ; (3) that it re- 
sults from the pressure of the iris upon the front face of 
the lens, for under these circunistances the hinder face of 
the lens would not remain stationary. This last hypothesis 
is further negatived by the fact that adjustment takes place 
equally well when the iris is absent. 

One other explanation remains, which is, in all proba- 
bility, the true one, though not altogether devoid of diffi- 
culties. The lens, which is very elastic, is kept habitually 
in a state of tension by the elasticity of its suspensory liga- 
ment, and consequently has a flatter form than it would 
take if left to itself. If the ciliary muscle contracts, it 
must, as has been seen, relax that ligamenl, and thereby 
diminish its elastic tension upon the lens. The lens, con- 
sequently, will become more convex, returning to its former 
Bhape when the ciliary muscle ceases to contract, and allows 
the choroid to return to its ordinary place. 

If this be the true explanation of adjustment, the sense 
of effort we feel must arise from the contraction of the 
ciliary muscle. 

284. Limits of the Power of Adjustment. — Adjustment 

can take place only within a certain range, which admits 
of great individual variation-. As a rule, no object which 



264 ELEMENTARY PHYSIOLOGY. 

is brought within less than about ten inches of the eye can 
be seen distinctly without effort. 

But many persons are born with the surface of the 
cornea more convex than usual, or with the refractive 
power of the eye increased in some other way ; while, 
very generally, as age draws on, the cornea flattens. In 
the former case, objects at ordinary distances are seen in- 
distinctly, because these images fall not on the retina, but 
in front of it ; while, in the latter, the same indistinctness 
is the result of the rays of light striking upon the retina 
before they have been brought to a focus. The defect of 
the former, or short-sighted people, is amended by wearing 
concave glasses, which cause the rays to diverge ; of the 
latter, or long-sighted people, by w r earing convex glasses, 
which make the rays converge. 

In the water camera the image brought to a focus on 
the screen at the back is inverted / the image of a tree, for 
instance, is seen with the roots upwards and the leaves and 
branches hanging downwards. The right of the image 
also corresponds with the left of the object, and vice versa. 
Exactly the same thing takes place in the eye with the 
image focussed on the retina, It, too, is inverted. (See 
300.) 

Sectiox V. — Appendages of the Eyeball. 

285, Muscles of the Eyeball. — The muscles which move 
the eyeball are altogether six in number — four straight 
muscles, or recti, and two oblique muscles, the obliqui 
(Fig. 97). The straight muscles are attached to the back 
of the orbit, round the edges of the hole through wmich 
the optic nerve passes, and run straight forward to their 
insertions into the sclerotic — one, the superior rectus, in 
the middle line above; one, the inferior, opposite it be- 
low ; and one half-way on each side, the external and in- 
ternal recti. The eyeball is completely embedded in fat 
behind and laterally ; and these muscles turn it as on a 



APPENDAGES OF THE EYEBALL. 



205 



cushion; the superior rectus inclining the axis of the eve 
upwards, the inferior downwards, the external outwards, 
the internal inwards. 

The two oblique muscles are both attached on the outer 
side of the ball, and rather behind its centre; and they 
both pull in a direction from the point of attachment tow- 
ards the inner side o^l the orbit — the lower, because it ai is 
here; the upper, because, though it arises along with the 




C.h. m 



Fi<;. 07. 



A. the musoles of the risrht eyeball viewed from above, and B of the left eyeball 
red from the outer Bid : s A'., the superior rectos; Inf. U.. the inferior rectus; 
I ' JL. Iu.li.. the external rectos; S.Oh., toe superior obttqoe; Iv/.Ob^ the inferior ob- 
lique: < '//.. the chiasm* <>t the optic oervea i//. »: ///.. the third nerve which BOppltea 
all the muscles except the superior oblique and the external rectos. 



recti from the back of the orbit, yet, after passing forwards 
and becoming tendinous at the upper and inner corner of 
the orbit, it traverses a pulley-like loop of ligament, and 
then turns downwards and outwards to itfi insertion. The 
action of the oblique muscles is somewhat complicated, but 
their general tendency is to roll the eyeball on its axis, and 

pull it a little forward and inward. 

286. The Eyelids. — The eyelid* are folds of skin con- 
taining thin plates of cartilage, and (ringed ai their edg 
with hair — the eyekuhi i — and with b series of small glands 
called Meibomian. Circularly-disposed fibres of striped 



266 ELEMENTARY PHYSIOLOGY. 

muscle lie beneath the integuments of the eyelids, and con- 
stitute the orbicularis muscle which shuts them. The 
upper eyelid is raised by a special muscle, the levator of 
the upper lid, which arises at the back of the orbit and 
runs forwards to end in the lid. 

The lower lid has no special depressor. 




Or 5. 



Fie. 9a 

The front view of the right eye dissected to show, Orb^ the orbicular muscle < i f the 
evelids; the pulley and insertion of the Buperior oblique, S.Ob.. and the interior oblique. 
inf. Ob. ; L.G., the lachrymal gland. 

287. The Lachrymal Apparatus. — At the edge of the 
eyelids the integument becomes continuous with a deli- 
cate, vascular, and highly-nervous mucous membrane, the 
conjunctiva, which lines the interior of the lids and the 
front of the eyeball, its epithelial layer being even con- 
tinued over the cornea. The numerous small ducts of a 
gland which is lodged in the orbit, on the outer side of the 
ball (Fig. 98, i. 6r.), the lachrymal gland, constantly pour 
its watery secretion into the interspace between the con- 
junctiva lining the upper eyelid and that covering the 
ball. On the inner side of the eye is a reddish fold, the 
caruncula lachry mails, a sort of rudiment of that third 
eyelid which is to be found in many animals. Above and 
below, close to the caruncula, the edge of each eyelid pre- 
sents a minute aperture (the punctum lachrymals), the 
opening of a small canal. The canals from above and be- 






COMPOUND SENSATIONS. 



'207 



low converge and open into the lachrymal sac; the upper 
blind end of a duet (Z.Z>., Fig. 99), which passes down 
from the orbit to the nose, opening below the inferior tur- 
binal bone (Fig. 49, h). It is through this system of canals 




-L.G. 



Fig. 00. 

A front view of the left eye. with the eyelids partially dissected to show lachrymal 
giand, L.G., and lachrymal duet. L.D. 

that the conjunctival mucous membrane is continuous with 
that of the nose ; and it is by them that the secretion of 
the lachrymal canal is ordinarily carried away as fast as 
it forms. 

But, under certain circumstances, as when the conjunc- 
tiva is irritated by pungent vapors, or when painful emo- 
tions arise in the mind, the secretion of the lachrymal gland 
exceeds the drainage-power of the lachrymal duct, and the 
fluid, accumulating between the lids, at length overflows 
in the form of tears. 



CHAPTER X. 

SENSATIONS AND JUDGMENT. 

Se< noil 1. — Compound Sensations, 

288. Our Sensations mostly Composite. — In explaining 
the (unctions of the sensory organs, I have hitherto con- 
fined myselfto describing the means by which the physical 
agent of a sensation i> enabled to irritate a given sensory 



268 ELEMENTARY PHYSIOLOGY. 

nerve ; and to giving some account of the simple sensations 
which are thus evolved. 

Simple sensations of this kind are such as might be pro- 
duced by the irritation of a single nerve-fibre, or of several 
nerve-fibres by the same agent. Such are the sensations 
of contact, of warmth, of sweetness, of an odor, of a musical 
note, of whiteness, or redness. 

But very few of our sensations are thus simple. Most 
of even those which we are in the habit of resrardino* as 
simple, are really compounds of different sensations, or of 
sensations with ideas, or with judgments. For example, 
in the preceding cases, it is very difficult to separate the 
sensation of contact from the judgment that something is 
touching us ; of sweetness, from the idea of something in 
the mouth; of sound or light, from the judgment that 
something outside us is shining, or sounding. 

289. Sensations of Smell the Simplest. — The sensations 
of smell are those which are least complicated by acces- 
sories of this sort. Thus, particles of musk diffuse them- 
selves with great rapidity through the nasal passages, and 
give rise to the sensation of a powerful odor. But beyond 
a broad notion that the odor is in the nose, this sensation 
is unaccompanied by any ideas of Jocality and direction. 
Still less does it give rise to any conception of form, or 
size, or force, or of succession, or contemporaneity. If a 
man had no other sense than that of smell, and musk were 
the only odorous body, he could have no sense of outness 
— no power of distinguishing between the external world 
and himself. 

290. Analysis of a Tactile Sensation. — Contrast this 
with what may seem to be the equally simple sensation 
obtained by drawing the finger along the table, the eyes 
being shut. This act gives one the sensation of a flat, hard 
surface outside one's self, which appears to be just as simple 
as the odor of musk, but is really a complex state of feel- 
ing compounded of : 






COMPOUND SENSATION'S. 269 

(</) Pure sensations of contact, 

(A) Pure muscular sensations of two kinds — the one 
arising from the resistance of the table, the other from the 
actions of those muscles which draw the finger along. 

(c) Ideas o( the order in which these pure sensations 
Bucceed one another. 

(</) Comparisons of these sensations and their order, 
with the recollection of like sensations similarly arranged, 
which have been obtained on previous occasions. 

(< ) Recollections of the impressions 'of extension, flat- 
ness, etc., made on the organ of vision when these previous 
tactile and muscular sensations were obtained. 

Thus, in this case, the only pure sensations are those 
of contact and muscular action. The greater part of what 
we call the sensation is a complex mass of present and 
rec Jlected ideas and judgments. 

291. Complexity of the Notion of Roundness. — Should 
any doubt remain that we do thus mix up our sensations 
with our judgments into one indistinguishable whole, shut 
the eyes as before, and, instead of touching the table with 
the finger, take a round lead-pencil between the fingers, 
and draw that along the table. The "sensation" of a flat 
hard surface will be just as clear as before; and yet all 
that we touch is the round surface of the pencil, and the 
only pure sensations we owe to the table are those afforded 
by the muscular sense. In fact, in this case, our "sensa- 
tion" of a flat hard surface is entirely a judgment based 
upon what the muscular sense tells us is going on in cer- 
t.iin muscles. 

A -til! more striking case of the tenacity with which 
we adhere to complex judgments, which we conceive t<> !>c 
pure sensations, and arc unable to analyze otherwise than 
by ;i pro* — of abstract reasoning, is afforded by our sense 
of roundness. 

Any one taking a marble between two lingers will say 

that he feels it to 1"' a single round body ; and he will 



270 ELEMENTARY PHYSIOLOGY. 

probably be as much at a loss to answer the question how 
he knows that it is round, as he would be if he were asked 
how he knows that a scent is a scent. 

Nevertheless, this notion of the roundness of the marble 
is really a very complex judgment, and that it is so may 
be shown by a simple experiment. If the index and middle 
fingers be crossed, and the marble placed between them, 
so as to be in contact with both, it is utterly impossible to 
avoid the belief that there are two marbles instead of one. 
Even looking at the marble, and seeing that there is only 
one, does not weaken the apparent proof derived from 
touch that there are two. 1 

The fact is, that our notions of singleness and round- 
ness are, really, highly complex judgments based upon a 
few simple sensations ; and, when the ordinary conditions 
of those judgments are reversed, the judgment is also re- 
versed. 

With the index and middle fingers in their ordinary 
position, it is, of course, impossible that the outer sides of 
each should touch opposite surfaces of one spheroidal body. 
If, in the natural and usual position of the fingers, their 
outer surfaces simultaneously give us the impression of a 
spheroid (which itself is a complex judgment), it is in the 
nature of things that there must be two spheroids. But, 
when the fingers are crossed over the marble, the outer 
side of each finger is really in contact with a spheroid ; 
and the mind, taking no cognizance of the crossing, judges 
in accordance with its universal experience, that two sphe- 
roids, and not one, give rise to the sensations which are 
perceived. 

Section II. — Delusions of Judgment. 

292. There are no "Delusions of the Senses." — Phe- 
nomena of this kind are not uncommonly called delusions 

1 A ludicrous form of this experiment is to apply the crossed finders to the end of 
the nose, when it at once appears double; and. in spite of the absurdity of the convic- 
tion, the mind cannot expel it, so long 1 as the sensations last. 



DELUSIONS OF JUDGMENT. 271 

of the senses,* but there is no such thing as a fictitious, or 
delusive, sensation. A sensation must exist to be a sensa- 
tion, and, it' it exists, it is real and not delusive. But the 
judgments we form respecting the causes and conditions 
of the sensations of which we are aware, are very often 
erroneous and delusive enough ; and such judgments may 
be brought about in the domain (^' every sense, either by 
artificial combinations (A sensations, or by the influence of 
unusual conditions of the body itself. The latter give rise 
to what are called subjective sensations. 

Mankind would be subject to fewer delusions than they 
are, if they constantly bore in mind their liability to false 
judgments due to unusual combinations, either artificial or 
natural, of true sensations. Men say: "I felt," "I heard," 
" I saw n such and such a thing, when, in ninety-nine cases 
out of a hundred, what they really mean is that they 
judge that certain sensations of touch, hearing, or sight, 
of winch they were conscious, were caused by such and 
BUcfa thil 

293, Subjective Sensations. — Among subjective sensa* 
turns within the domain of touch, are the feelings of creep- 
ing and prickling of the skin, which are not uncommon in 

tain states of the circulation. The subjective evil smells 
and bad tastes which accompany some diseases are very 
probably due to similar disturbances in the circulation of 
the sensory organs of smell and taste. 

Many persons arc liable to what may be called a uditW // 

spectra — music of various degrees of complexity sounding 

in their ears, without any external cause, while they are 

wide awake. 1 know not if other persons are similarly 
troubled, but, in reading books written by persons with 
w1m.ui I am acquainted, I am sometime- tormented by 
bearing tin- words pronounced in the exact way in which 
these persons would utter them, any trick or peculiarity 
of voir.-. or gesture, being also very accurately reproduced. 
i I suppose thai every one must have been startled, ;>t 



272 ELEMENTARY PHYSIOLOGY. 

times, by the extreme distinctness with which his thoughts 
have embodied themselves in apparent voices. 

The most wonderful exemplifications of subjective sen- 
sation, however, are afforded by the organ of sight. 

Any one who has witnessed the sufferings of a man 
laboring under delirium tremens (a disease produced by 
excessive drinking), from the marvelous distinctness of 
his visions, which sometimes take the forms of devils, 
sometimes of creeping animals, but almost always of some- 
thing fearful or loathsome, will not doubt the intensity of 
subjective sensations in the domain of vision. 

294. Remarkable Case of Delusive Appearances. — But 
that illusive visions of great distinctness should appear, it 
is not necessary for the nervous system to be thus obviously 
deranged. People in the full possession of their faculties, 
and of high intelligence, may be subject to such appear- 
ances, for which no distinct cause can be assigned. An 
excellent illustration of this is the famous case of Mrs. A., 
given by Sir David Brewster in his " Natural Magic : " 

" (1) The first illusion to which Mrs. A. was subject, 
was one which affected only the ear. On the 21st of De- 
cember, 1830, about half-past four in the afternoon, she was 
standing near the fire in the hall, and on the point of going 
up to dress, when she heard, as she supposed, her husband's 

voice calling her by name : ' , , come here ! come 

to me ! ' She imagined that he was calling at the door to 
have it opened ; but, upon going there and opening the 
door, she was surprised to find no person there. Upon 
returning to the fire she again heard the same voice call- 
ing out very distinctly and loudly, 4 , come, come 

here ! ' She then opened two other doors of the same 
room, and, upon seeing no person, she returned to the fire- 
place. After a few moments she heard the same voice still 
calling, ' Come to me, come ! come away ! ' in a loud, plain- 
tive, and somewhat impatient tone ; she answered as loud- 
ly, ' Where are you ? I don't know where you are,' still 



DELUSIONS OF JUDGMENT. 273 

imagining that be was somewhere in search of her; but, 
receiving no answer, she shortly went up-stairs. On Mr. 
A.V return to the house, about half an hour afterwards, 
she inquired why he had called her so often, and where he 
was, and she was ol course greatly surprised to learn that 
he had not been near the house at the time. A similar 
illusion, which excited no particular notice at the time, 
occurred to Mrs. A. when residing at Florence, about 
ten years before, and when she was in perfect health. 
When she was undressing after a ball, she heard a voice 
call her repeatedly by name, and she was at that time un- 
able to account for it. 

'* ("2) The next illusion which occurred to Mrs. A. was 
of a more alarming character. On the 30th of December, 
about four o'clock in the afternoon, Mrs. A. came down- 
stairs into the drawing-room, w.hich she had quitted only 
a few minutes before, and, on entering the room, she saw r 
her husband, as she supposed, standing with his back to 
the fire. As he had gone out to take a walk about half 
an hour before, she was surprised to see him there, and 
asked him why he had returned so soon. The figure looked 
fixedly at her with a serious and thoughtful expression of 
countenance, but did not speak. Supposing that his mind 
was absorbed in thought, she sat down in an arm-chair near 
the fire, and within two feet, at most, of the figure, which 
she still saw stant ling before her. As its eyes, however, still 
continued to be fixed upon her, she said, after a lapse of a 
few minutes, 'Why don't you speak?' The figure imme- 
diately moved off towards the window at the farther end 
of the loom, with it- eyes "'ill gazing On her, and it passed 

• tv close to her in doing ><>, that she was struck with 

the circumstance of hearing no step or sound, nor feeling 
her clothes brushed against, dot even any agitation in 

the air-. 

•• Although she was now convinced that the figure was 
not her husband, ye\ %he never for a moment supposed thai 

18 



274 ELEMENTARY PHYSIOLOGY. 

it was any thing supernatural, and was soon convinced that 
it was a spectral illusion. As soon as this conviction had 
established itself in her mind, she recollected the experi- 
ment which I had suggested of trying to double the ob- 
ject ; but, before she was able distinctly to do this, the 
figure had retreated to the window, where it disappeared. 
Mrs. A. immediately followed it, shook the curtains, and 
examined the window, the impression having been so dis- 
tinct and forcible, that she was unwilling to believe that it 
was not a reality. Finding, however, that the figure had 
no natural means of escape, she was convinced that she had 
seen a spectral apparition like that recorded in Dr. Hum- 
bert's work, and she consequently felt no alarm or agita- 
tion. The appearance was seen in bright daylight, and 
lasted four or five minutes. When the figure stood close 
to her, it concealed the real objects behind it, and the ap- 
parition was fully as vivid as the reality. 

" (3) On these two occasions Mrs. A. was alone, but, 
when the next phantom appeared, her husband was pres- 
ent. This took place on the 4th of January, 1830. About 
ten o'clock at night, when Mr. and Mrs. A. were sitting in 
the drawing-room, Mr. A. took up the poker to stir the 
fire, and, when he was in the act of doing this, Mrs. A. ex- 
claimed, 4 Why, there's the cat in the room ! ' c Where ?' 
exclaimed Mr. A. c There — close to you,' she replied. 
' Where ? ' he repeated. ' Why, on the rug, to be sure, 
between yourself and the coal-scuttle.' Mr. A., who still 
had the poker in his hand, pushed it in the direction men- 
tioned. ' Take care ! ' cried Mrs. A., i take care ! you are 
hitting her with the poker.' Mr. A. again asked her to 
point out exactly where she saw the cat. She replied, 
' Why, sitting up there close to your feet on the rug ; she 
is looking at me. It is Kitty — come here, Kitty ! ' There 
were two cats in the house, one of which went by this 
name, and they were rarely, if ever, in the drawing-room. 

"At this time Mrs. A. had no idea that the sio4it of the 






DELUSIONS OF JUDGMENT. 275 

cat was an illusion. When she was asked to touch it, she 
got up for the purpose, and seemed as it' she was pursuing 

something which moved away. She followed a tew steps, 
and then said, k It has gene under the chair." Mr. A. as- 
sured her that it was an illusion, hut she would not believe 
it. He then lifted up the chair, and Mis. A. saw nothing 
more of it. The room was searched all over, and nothing 
found in it. There was a clog lying on the hearth, who 
would have betrayed great uneasiness if a cat had been in 
tlTe room, but he lav perfectly quiet. In order to be quite 
certain, Mr. A. rang the bell, and sent for the cats, both of 
which were found in the house-keeper's room. 

w (4) About a month after this occurrence, Mrs. A., 
who had taken a somewhat fatiguing drive during the day, 
vis preparing to go to bed about eleven o'clock at night, 
and, sitting before the dressing-glass, was occupied in ar- 
ranging her hair. She was in a listless and drowsy state 
of mind, but fully awake. When her ringers were in active 
motion among the papillotes, she was suddenly startled by 
- ing in the mirror the figure of a near relative, who was 
then in Scotland, and in perfect health. The apparition 
appeared over her left shoulder, and its eves met hers 
in the glass. It was enveloped in grave-clothes, closely 
pinned, as is usual with corpses, round the head and under 
the chin; and, though the eyes were open, the features 
were solemn and rigid. The dress was evidently a shroud, 

Mrs. A. remarked even the punctured pattern usually 
worked in a peculiar manner round the edges of that gar- 
ni ent. lira A. described herself as, at the time, sensible 

i feeling like what we conceive of fascination, compel- 
ling h<*r, for the time, to gaze upon this melancholy appa- 
rition, which was as distinci and vivid as any reflected 
reality c tuld he, the light of the candle noon the dressing- 
table appearing to shine fully upon it- face. After a few 

mi i iut"- she turned round to look for- the reality of the form 

r her shoulder, but it was not visible, and it had also 



276 ELEMENTARY PHYSIOLOGY. 

disappeared from the glass when she looked again in that 
direction. 

" (7) On the 17th of March, Mrs. A. was preparing for 
bed. She had dismissed her maid, and was sitting with 
her feet in hot water. Having an excellent memory, she 
had been thinking upon and repeating to herself a striking 
passage in the Edinburgh Review, when, on raising her 
eyes, she saw seated in a large easy-chair before her the 
figure of a deceased friend, the sister of Mr. A. The figure 
was dressed, as had been usual with her, with great neat- 
ness, but in a gown of a peculiar kind, such as Mrs. A. had 
never seen her wear, but exactly such as had been de- 
scribed to her by a common friend as having been worn 
by Mr. A.'s sister during her last visit to England. Mrs. 
A. paid particular attention to the dress, air, and appear- 
ance of the figure, which sat in an easy attitude in the 
chair, holding a handkerchief in one hand. Mrs. A. tried 
to speak to it, but experienced a difficulty in doing so, and 
in about three minutes the figure disappeared. 

"About a minute afterwards, Mr. A. came into the 
room, and found Mrs. A. slightly nervous, but fully aware 
of the delusive nature of the apparition. She described it 
as having all the vivid coloring and apparent reality of 
life ; and for some hours preceding this and other visions, 
she experienced a peculiar sensation in her eyes, which 
seemed to be relieved when the vision had ceased. 

" (9) On the 11th of October, when sitting in the draw- 
ing-room, on one side of the fireplace, she saw the figure 
of another deceased friend moving towards her from the 
window at the farther end of the room. It approached 
the fireplace, and sat down in the chair opposite. As there 
were several persons in the room at the time, she describes 
the idea uppermost in her mind to have been a fear lest 
they should be alarmed at her staring, in the way she was 



DELUSIONS OF JUDGMENT. i>7 7 

conscious of doing, at vacancy, and should fancy her intel- 
lect disordered. Under the influence of this fear, and 
recollecting a story of a similar effect in your 1 work on 
• Demonology,' which she had lately read, she summoned 
up the requisite resolution to enable her to cross the space 
before the fireplace, and seal herself in the same chair with 
the figure. The apparition remained perfectly distinct till 
she sat down, as it were, in its lap, when it vanished." 

295. Personal Characteristics. — It should be mentioned 
that Mrs. A. was naturally a person of very vivid imagina- 
tion, and that, at the time the most notable of these illu- 
sions appeared, her health was weak from bronchitis and 
enfeebled digestion. 

It is obvious that nothing but the singular courage and 
clear intellect of Mrs. A. prevented her from becoming a 
mine of ghost-stories of the most excellently authenticated 
kind. And the particular value of her history lies in its 
showing that the clearest testimony of the most unim- 
peachable witness may be quite inconclusive as to the 
objective reality of something which the witness has seen. 

296. The Senses not at Fault.— Mrs. A. undoubtedly 
saw what she said she saw. The evidence of her eyes as 
to the existence of the apparitions, and of her ears to those 
of the voices, was, in itself, as perfectly trustworthy as 
their evidence would have been had the objects really ex- 
isted For there can be no doubt that exactly those parts 
of her retina which would have been affected by the image 
of a cat, and those parts of her auditory organ which would 
have been set vibrating by her husband's voice, or the por- 
tions of the sensorium with which those organs of sense 
are connected, were thrown into a corresponding state of 
activity by some internal cause. 

What the Sen8es testify IS neither more nor less than 
the fad of their own affection. As to the cause of that 

tan OB Natural Iflgfe" 



278 ELEMENTARY PHYSIOLOGY. 

affection they really say nothing, but leave the mind to 
form its own judgment on the matter. A hasty or super- 
stitious person in Mrs. A.'s place would have formed a 
wrong judgment, and would have stood by it on the plea 
that " she must believe her senses." 

297. Ventriloquism. — The delusions of the judgment, 
produced not by abnormal conditions of the body, but by 
unusual or artificial combinations of sensations, or by sug- 
gestions of ideas, are exceedingly numerous, and occasion- 
ally are not a little remarkable. 

Some of those which arise out of the sensation of touch 
have already been noted. 1 do not know of any produced 
through smell or taste, but hearing is a fertile source of 
such errors. 

What is called ventriloquism (speaking from the belly), 
and is not uncommonly ascribed to a mysterious power of 
producing voice somewhere else than in the larynx, de- 
pends entirely upon the accuracy with which the performer 
can simulate sounds of a particular character, and upon 
the skill with which he can suggest a belief in the exist- 
ence of the causes of these sounds. Thus if the ventrilo- 
quist desire to create the belief that a voice issues from 
the bowels of the earth, he imitates with great accuracy 
the tones of such a half-stifled voice, and suggests the ex- 
istence of some one uttering it by directing his answers 
and gestures towards the ground. These gestures and 
tones are such as would be produced by a given cause ; 
and no other cause being apparent, the mind of the by- 
stander insensibly judges the suggested cause to exist. 

Section III. — Visual Sensations and Mental States. 

298. Optical Delusions. — The delusions of the judgment 
through the sense of sight — optical delusions, as they are 
called — are more numerous than any others, because such 
a great number of what we think to be simple visual sen- 
sations are really very complex aggregates of visual sen- 



VISUAL SENSATIONS AND MENTAL STATES. 279 

sat ions, tactile sensations, judgments, and recollections of 
former sensations and judgments. 

It will be instructive to analyze 1 some of these judg- 
ments into their principles, and to explain the delusions 
by the application of these principles. 

299. Externality of Visible Objects. — When an exter- 
nal body is felt by the touch to be in a given place y the 
image of that body falls on a point of the retina which 
lies at one end of a straight line joining the body and the 
r>t'u<<i s and traversing a particular region of the centre of 
tin eye, litis straight line is called the optic axis. 

Conversely, icJioi any part of the surface of the retina 
xcitedj tin luminous sensation is referred by the mind 
t<> sonu point outside the body, In the dm ection of the optic 
axis. 

It is for this reason that when a phosphene is created 
by pressure, say on the outer and lower side of the eye- 
ball, the luminous image appears to lie above, and to the 
inner side of, the eye. Any external object which could 
produce the sense of light in the part of the retina pressed 
upon must, owing to the inversion of the retinal images 
(284), in fact occupy this position; and hence the mind 
refers the light seen to an object in that position. 

300. The Inversion of the Visual Images. — The same 
kind of explanation is applicable to the apparent paradox 
that, while all the pictures of external objects are certainly 
inverted on the retina by the refract ing media of the eye, 
we nevertheless see them upright. It is difficult to under- 
stand this, until one reflects that the retina has, in itself, 
no means of indicating to the mind which of it- pan- lies 

at the top. and which at t he bot torn ; and that the mind 

learns to call an impression on the retina high or low, 
riiiht or left, simply on account of the association of such 
an impression with certain coincident tactile impressions. 

In Other words, when one part of the retina 18 affected, the 

object causing the affection is found to be near the right 



280 ELEMENTAHY PHYSIOLOGY. 

hand ; when another, the left ; when another, the hand 
has to be raised to reach the object ; when yet another, it 
has to be depressed to reach it, And thus the several im- 
pressions on the retina are called right, left, upper, lower, 
quite irrespectively of their real positions, of which the 
mind has, and can have, no cognizance. 

301. Correspondence of Objects and Images. — When 
an external body is ascertained by touch to be simple, it 
forms but one image on the retina, of a single eye ; and, 
when two or more images fall on the retina of a single 
eye, they ordinarily proceed from a corresponding number 
of bodies which are distinct to the touch. 

Conversely, the sensation of tico or more images is 
judged by the mind to proceed from two or more objects. 

If two pin-holes be made in a piece of card-board at a 
distance less than the diameter of the pupil, and a small 
object like the head of a pin be held pretty close to the 
eye, and viewed through these holes, two images of the 
head of the pin will be seen. The reason of this is, that 
the rays of light from the head of the pin are split by the 
card into two minute pencils, which pass into the eye on 
either side of its centre, and cannot be united again and 
brought to one focus on account of the nearness of the 
pin to the eye. Hence they fall on different parts of the 
retina, and each pencil of rays, being very small, makes a 
tolerably distinct image of its own of the pin's head on 
the retina. Each of these images is now referred outward 
(299) in the direction of the appropriate optic axis, and 
two pins are apparently seen instead of one. A like ex- 
planation applies to multiplying -glasses and doubly -refract- 
ing crystals, both of which, in their own ways, split the 
pencils of light proceeding from a single object into two 
or more separate bundles. These give rise to as many 
images, each of which is referred by the mind to a distinct 
external object. 

302. Judgment of Distance—Perspective. — Certain vis- 



VISUAL SENSATIONS AND MENTAL STATES. 281 

ual phenomena ordinarily accompany thosi products of 
tactil sensation to which uh giv\ th< nam* of size, dis- 
tance, and form. Thus, other things being alike, the 
f the retina covered by thi image of a large object 

larger than that covered by a small olyeet : while that 
I by a near object is larger than that covered by a 
distant object ; and, other conditions bi ing aiiJa a near 
Meet is more brilliant than a distant one. Furthermore, 
the shadows of objects differ with the forms of their sur* 
faces, as determined by touch. 

Conversely, if these visual sensations can h produced, 
th<i/ inevitably suggest a belief in the existence of objects 
competent to produce tin corresponding tactile sensations. 

What is called perspective, whether solid or aerial, in 
drawing, or painting, depends on the application of these 
principles. It is a kind of visual ventriloquism — the 
painter putting upon his canvas all the conditions requisite 
tor tin 1 production of images on the retina, having the size, 
relative form, and intensity of color of those which would 
actually be produced by the objects themselves in Xature. 
And the success of his picture, as an imitation, depends 
upon the closeness of the resemblance between the images 
it produces on the retina, and those which would be pro- 
duced by the objects represented. 

303. Magnifying-Glasses,— To most persons the image 
of a pin, at live or six inches from the eye, appears blurred 
and indistinct— the eye not being capable m' adjustment to 

ahoH a focus. If a small hole be made in a piece of 

i. the circumferential rays which cause the blur are rut 

Off, and the image become- distinct. Bui at the same time 

it i- magnified, or look- bigger, because the image of the 

pin. in spite of the loss of the circumferential rays, occupies 

luch larger extent of the retina when dose than when dis- 
tant. All convex glasses produce the Bame effeci — while 
diminish the apparent size of ao object, be* 
ise they diminish the size n f its image on the retina. 



282 ELEMENTARY PHYSIOLOGY. 

304. Why the Sun and Moon look larger near the 
Horizon. — The moon, and the sun, when near the horizon, 
appear very much larger than they are when high in the 
sky. When in the latter position, in fact, we have nothing 
to compare them with, and the small extent of the retina 
which their images occupy suggests small absolute size. 
But, as they set, we see them passing behind great trees 
and buildings which we know to be very large and very 
distant, and yet occupying a larger space on the retina 
than the latter do. Hence the vague suggestion of their 
larger size. 

305. Judgment of Form by Shadows. — If a convex sur- 
face be lighted from one side, the side towards the light is 
bright — that turned from the light, dark, or in shadow ; 
while a concavity is shaded on the side towards the light, 
bright on the opposite side. 

If a new half-crown, or a medal with a well-raised head 
upon its face, be lighted sideways by a candle, we at once 
know the head to be raised (or a cameo) by the disposition 
of the light and shade ; and if an intaglio* or medal on 
which the head is hollowed out, be lighted in the same 
way, its nature is as readily judged by the eye. 

But now, if either of the objects thus lighted be viewed 
with a convex lens, which inverts its position, the light and 
dark sides will be reversed. With the reversal the judg- 
ment of the mind will change, so that the cameo will be 
regarded as an intaglio, and the intaglio as a cameo ; for 
the light still comes from w^here it did, but the cameo ap- 
pears to have the shadows of an intaglio, and vice versa. 
So completely, however, is this interpretation of the facts 
a matter of judgment, that, if a pin be stuck beside the 
medal so as to throw a shadow, the pin and its shadow, 
being reversed by the lens, will suggest that the direction 
of the light is also reversed, and the medals will seem to 
be what they really are. 

306. Judgment of Changes of Form. — Whenever an ex- 



VISUAL SENSATIONS AND MENTAL STATES. 283 

ternal object is watched rapidly changing its form, a con- 
tinuous series of different pictures of thi object is impressed 
upon the smut spot of the retina. 

Conversely, if a continuous series of different pictures 

\m object is impressed upon one pari of the retina, the 
nd judges that they an due to a singU external object, 
undergoing changes of form. 

This is the principle of the curious toy culled the than- 
Urope, or "zootrope," or "wheel of life," by the help of 
which, on looking through a hole, one sees images of jug- 
glers throwing up and catching balls, or boys playing at 
leap-frog over one another's backs. This is managed by 
painting at intervals, on a disk of card, figures and jugglers 
in the attitudes of throwing, waiting to catch, and catch- 
ing ; or boys "giving a back," leaping, and coming into 
position after leaping. The disk is then made to rotate 
before an opening, so that each image shall be presented 
for an instant, and follow its predecessor before the im- 
pression of the latter has died away. The result is that 
the succession of different pictures irresistibly suggests 
one or more objects undergoing succes-ive changes — the 
juggler seems to throw the balls, and the boy r s appear to 
jump over one another's backs. 

307. Single Vision with Two Eyes. — When an exter- 
nal object is ascertained by touch to be single, the centres 
of its retinal images in t/<> two eyes fall upon the centres 
of thi yellow spots of tin /wo eyes, when both eyes an 
directed towards it; W, if there be two external objects, 
tin centres of both their images cannot faU, at the samt 
time, upon the centres of thi yellow spots* 

Conversely, when the centres of two images, formed 
simtdtaneously in '/<< two eyes, fall upon the centres of 
tf lt yellow spots, thi mind judges thi images to i>< caused 
by </ singU external <>hj<<-t « hut if not, by two. 

Thi- seei 1 1- to i><- the only admissible explanation of the 
(acts, thai an objeel which appears single to the touch and 



284 ELEMENTARY PHYSIOLOGY. 

when viewed with one eye, also appears single when it is 
viewed with both eyes, though two images of it are neces- 
sarily formed ; and on the other hand, that when the cen- 
tres of the two images of one object do not fall on the 
centres of the yellow spots, both images are seen sepa- 
rately, and we have double vision. In squinting, the axes 
of the two eyes do not converge equally towards the object 
viewed. In consequence of this, when the centre of the 
image formed by one eye falls on the centre of the yellow 
spot, the corresponding part of that formed by the other 
eye does not, and double vision is the result. 

For simplicity's sake we have supposed the images to 
fall on the centre of the yellow spot. But, though vision is 
distinct only in the yellow spot, it is not absolutely limited 
to it ; and it is quite possible for an object to be seen as a 
single object w T ith two eyes, though its images fall on the 
two retinas outside the yellow spots. All that is neces- 
sary is that the two spots of the retinas on which the 
images fall should be similarly disposed towards the cen- 
tres of their respective yellow spots. Any two points of 
the two retinas thus similarly disposed towards their re- 
spective yellow spots (or more exactly to the points in 
which the optic axes end), are spoken of as corresponding 
points ; and any two images covering two corresponding 
areas are conceived of as coming from a single object. It 
is obvious that the inner (or nasal) side of one retina cor- 
responds to the outer (or cheek) side of the other. 

308. The Pseudoscope. — In single vision with two eyes, 
the cixes of the two eyes, of the movements of which the 
muscular sense gives an indication, cut one another at a 
greater angle when the object approaches, at a less angle 
when it goes farther off. 

Conversely, if, without changing the position of an 
object, the axes of the two eyes ivhich view it can be made 
to converge or diverge, the object will seem to approach oi 
go farther off. 



VISUAL SENSATIONS AND MENTAL STATES. 285 

In the instrument called the pseudoscope, mirrors or 
prisms are disposed in such a manner that the angle at 
which rays of light from an object enter the two eyes, can 
be altered without any change in the object itself; and 
consequently the axes of these eyes are made to converge 
or diverge. In the former case the object seems to ap- 
proach ; in the latter, to recede. 

309. Judgment of Solidity— the Stereoscope. — When a 
body of moderate size, ascertained by towJi to be solid, 
<l irith both eyes, the images of it, formed by the 
two '//' s, <i,\ m cessarily different {one shoicing more of its 
right si<l< , the other of its left side). Xevertheless, they 
coalesce into a common image, icJiich gives the impression 
of solidity. 

Conversely, if the two images of the right and left 
aspects of a solid body be made to fall upon the retinas of 
the two eyes in such a way as to coalesce into a common 
image, they art judged by the mind to proceed from the 
single solid body which alone, under ordinary circum- 
stai competent to produce them. 

The stereoscope is constructed upon this principle. 
Whatever its form, it is so contrived as to throw the 
images of two pictures of a solid body, such as would be 
obtained by the right and left eye of a spectator, on to 
such parts of the retinas of the person who uses the 
stereoscope as would receive these images, if they really 
proceeded from one solid body. The mind immediately 
judges them to arise from a single external solid body, 
and h a solid body in place of the two pictures. 

The operation of the mind upon the sensations pre- 
sented to it by tin- two ey<>> i> exactly comparable to thai 
which takes place when, on holding a marble between the 

finger and thumb, we at oner declare it t«> be a single 

sphere (291), Thai which is absolutely presented to the 
mind by the sense of touch in this case is by no means 

the sensation of <>nc spheroidal body, but two distinct sen- 



286 ELEMENTARY PHYSIOLOGY. 

sations of two convex surfaces. That these two distinct 
convexities belong to one sphere, is an act of judgment, or 
process of unconscious reasoning, based upon many par- 
ticulars of past and present experience, of which we have, 
at the moment, no distinct consciousness. 



CHAPTER XI. 

THE NERVOUS SYSTEM AND INNERVATION. 

Section I. — The Spinal Cord — Reflex Actions. 

310, The General Nervous System. — The sensory or- 
gans are, as we have seen, the channels through which 
particular physical agents are enabled to excite the sen- 
sory nerves with which these organs are connected ; and 
the activity of these nerves is evidenced by that of the 
central organ of the nervous system, which activity be- 
comes manifest as a state of consciousness — the sensation. 

We have also seen that the muscles are instruments by 
which a motor nerve, excited by the central organ with 
which it is connected, is able to produce motion. 

The sensory nerves, the motor nerves, and the central 
organ, constitute the greater part of the nervous system, 
which, with its function of innervation, we must now study 
somewhat more closely, and as a whole. 

311. The Cerebro-Spinal and Sympathetic Systems. — 
The nervous apparatus consists of two sets of nerves and 
nerve-centres, which are intimately connected together and 
yet may be conveniently studied apart. These are the 
cerebrospinal system and the sympathetic system. The 
former consists of the cerebrospinal axis (composed of the 
brain and spinal cord) and the cerebral and spinal nerves, 
which are connected with this axis. The latter comprises 
the chain of sympathetic ganglia, the nerves which they 



THE SPINAL CORD— REFLEX ACTIONS. 287 

give off, and the nervous cords by which they are con- 
nected with one another and with the cerobro-spinal nerves. 

312. Nerve-Fibres and Nerve-Centres. — Nerves are made 
up entirely of nerve-fibres, the structure of which is some- 
what different in the cerebro-spinal and in the sympathetic 
systems, (See 3^6.) Nerve-centres, on the other hand, 
are composed of nerve-cells or ganglionic corpuscles^ min- 
gled with nerve-fibres (356). Such cells, or corpuscles, are 
found in various parts of the brain and spinal cord, in the 
sympathetic ganglia, and also in the ganglia belonging to 
spinal nerves as well as in certain sensory organs, such as 
the retina and the internal ear. 

313. Membrane of the Cerebro-Spinal Axis. — The cere- 
brospinal axis lies in the cavity of the skull and spinal 
column, the bony walls of which cavity are lined by a very 
tough fibrous membrane, serving as the periosteum of the 
component bones of this region, and called the dura mater. 
The brain and spinal cord themselves are closely invested 
by a very vascular fibrous tissue, called pia mater. The 
numerous blood-vessels supplying these organs run for 
some distance in the pia mater, and, where they pass into 
the substance of the brain or cord, the fibrous tissue of the 
pia mater accompanies them to a greater or less depth. 

The outer surface of the pia mater and the inner sur- 
face of the dura mater pass into a delicate fibrous tissue, 
lined by an epithelium, which is called the arachnoid mem- 
brane. Thus one layer of arachnoid coats the brain and 
spinal cord, and another lines the dura mater. As these 
layers become continuous with one another at various 
points, the arachnoid forms a sort of shut sac, like the peri- 
cardium j and, in common with other serous membranes, 
it & a Quid, the arachnoid fluid) into its interior. 

The interspace between the internal and external layers 
of the arachnoid of the brain is, for the mosi part, very 

ill; that between the corresponding layers of the arach- 
noid of the spinal cord is larger. 



288 



ELEMENTARY PHYSIOLOGY. 



314. The Spinal Cord.— The spinal cord (Figs. 100, 101) 
is a column of grayish-white soft substance, extending 
from the top of the spinal canal, where it is continuous 
with the brain, to about the second lumbar vertebra, where 
it tapers off into a filament. A deep fissure, the anterior 
fissure (Fig. 102, 1), divides it in the middle line in front, 
nearly down to its centre : and a similar cleft, the posterior 
fissure (Fig. 102, 2), also extends nearly to its centre in the 
middle line behind. The pia mater extends into each of 
these fissures, and supports the vessels which supply the 
cord with blood. In consequence of the presence of these 
fissures, only a narrow bridge of the substance of the cord 
connects its two halves, and this bridge is traversed 
throughout its entire length by a minute canal, the centre 
canal of the cord (Fig. 102, 3). 

Each half of the cord is divided longitudinally into 
three equal parts, the anterior, lateral, and posterior col- 




,/CTJ 




Fig. 101. 



The Spinal Cord, 



Fig. 100.— A front view of a portion of the cord. On the right side, the anterior 
roots, A.R., are entire ; on the left side they are cut, to show the posterior roots, P.R. 

Fig. 101. — A transverse section of the cord. A, the anterior fissure; P, the pos- 
terior fissure; G, the central canal; C, the gray matter; IF, the white matter; A.R., 
the anterior root, PR., the posterior root, Gn., the ganglion, and T., the trunk, of a 
spinal nerve. 

uinns (Fig. 102, 6> 7, 8), by the lines of attachment of two 
parallel series of delicate bundles of nervous filaments, the 
roots of the spinal nerves. The roots of the nerves which 
arise along that line which is nearer the posterior surface 
of the cord are called posterior roots ; those which arise 
along the other line are the anterior roots. A certain 






THE SPINAL CORD— REFLEX ACTIONS. 289 

number of anterior and posterior roots, on the same level 
on each side of the cord, converge and form anterior and 
posterior bundles, and then the two bundles, anterior and 
posterior, coalesce into the trunk of a spinal nerve; but, 
before doing so, the posterior bundle presents an enlarge- 
ment - the ganglion of the posterior root. 

The trunks of the spinal nerves pass out of the spinal 
canal by apertures between the vertebra?, called the inter- 
vertebral foramina, and then divide and subdivide, their 
ultimate ramifications going for the most part to the mus- 
cles and to the skin. 

There are thirty-one pairs of these spinal nerves, and, 
consequently, twice as man}' sets of roots of spinal nerves 
given off, in two lateral series, from each half of the cord. 

315. Transverse Section of a Cord. — A transverse sec- 
tion of the cord (Figs. 101 and 102) shows that each half 
contains two substances — a white substance on the outside, 
and a grayish-red substance in the interior. And this gray 
m <itter, as it is called, is so disposed that, in a transverse 
section, it looks something like a crescent, with one end 
bigger than the other, and with the concave side turned 
outwards. The two ends of the crescents are called its 
Jin,-,,* or cornua (Fig. 102, e e), the one directed forwards 
bring the anterior cornu ; the one turned backwards the 
posterior cornu (Fig. 102, a a). The convex sides of the 
cornu of the gray matter approach one another, and are 
joined by the bridge which contains the central canal. 

Many of the nerve-fibres of which the anterior roots are 
composed may he traced into tlir anterior cornu, while 
those of the posterior roots enter the posterior cornu. 

316. Difference between Gray and White Matter. — 
There IS a fundamental difference in structure between the 

v and the white matter. The white matter consists en- 
tirely of nerve-fibres supported in a delicate framework 

connective tissue, and accompanied by blood-vessels. 
Most of these fibres run lengthways in the cord, and con- 
19 



290 



ELEMENTARY PHYSIOLOGY. 



sequently, in a transverse section, the white matter is really 
composed of a multitude of the cut ends of these fibres. 

The gray matter, on the other hand, contains, in addi- 
tion, a number of nerve-cells or ganglionic corpuscles, some 
of them of considerable size. These cells are wholly absent 
in the white matter. 

317. Physiological Properties of Nerves. — The physio- 




Fig, 102. 

Transverse Section of one-ha.lf of the Spinal Cord (en the Lumbar Region), 

magnified. 



1, anterior fissure; 2, posterior fissure; 3, central canal; 4 and 5, bridges connect- 
ing the two halves (posterior and anterior commissures) ; 6, posterior column ; 7, lat- 
eral column ; 8, anterior column; 9, posterior root; 10. anterior root of nerve. 

a, a, posterior horn of gray matter ; e, e, e, anterior horn of gray matter. Through 
,he several columns 6, T, and 8, each composed of white matter, are seen the prolonga- 
tions of the pia mater, which carry blood-vessels into the cord from the outside. The 
pia mater itself is seen over the whole of the cord. 



THE SPINAL CORD— REFLEX ACTIONS. 291 

logical properties of the organs now described are very 
remarkable. 

If the trunk of a spinal nerve be irritated in any way, 
as by pinching, cutting, galvanizing, or applying a hot 
body, two things happen : in the first place, all the muscles 
to which filaments of this nerve are distributed, contract; 
in the second, acute pain is felt, and the pain is referred to 
that part of the skin to which fibres of the nerve are dis- 
tributed. In other words, the effect of irritating the trunk 
of a nerve is the same as that of irritating its component 
fibres at their terminations. 

The effects just described will follow upon irritation of 
part of the branches of the nerve : except that, when a 
branch is irritated, the only muscles directly affected, and 
the only region of the skin to which pain is referred, will 
be those to which that branch sends nerve fibres. And 
these effects will follow upon irritation of any part of a 
nerve from its smallest .branches up to the point of its 
trunk, at which the anterior and posterior bundles of root- 
fibres unite. 

318. Functions of Anterior and Posterior Roots. — If the 
anterior bundle of root-fibres be irritated in the same way, 
only half the previous effects are brought about. That is 
to say. all the muscles to which the nerve is distributed 
contract, but no pain is felt. 

£ again if the posterior, ganglionated bundle be irri- 
tated, only half the effects of irritating the whole trunk is 
produced. But it is the other half ; that is to say, none 
of the muscles to which the nerve is distributed contract, 
but intense pain is referred to the whole area of skill to 

which the fibres of the nerve are distributed. 

It i- clear enough, from these experiments, that all the 
power of causing muscular contraction which a spinal 
nerve possesses, is lodged in the fibres which compose its 
anterior roots; and ;ill the power of giving rise to sensa- 
tion, in those of its posterior root-. Hence the {interior 



292 ELEMENTARY PHYSIOLOGY. 

roots are commonly called motor, and the posterior sen- 
sory. 

319, Experiment—Paralysis.— The same truth may be 
illustrated in other ways. Thus, if, in a living animal, the 
anterior roots of a spinal nerve be cut, the animal loses nil 
control over the muscles to which that nerve is distributed, 
though the sensibility of the region of the skin supplied by 
the nerve is perfect. If the posterior roots be cut, sensa- 
tion is lost, and voluntary movement remains. But, if both 
roots be cut, neither voluntary movement nor sensibility is 
any longer possessed by the part supplied by the nerve. 
The muscles are said to be paralyzed, and the skin may be 
cut, or burnt, without any sensation being excited. 

If, when both roots are cut, that end of the motor root 
which remains connected with the trunk of the nerve be 
irritated, the muscles contract ; while, if the other end be 
so treated, no apparent effect results. On the other hand, 
if the end of the sensory root connected with the trunk of 
the nerve be irritated, no apparent effect is produced, while, 
if the end connected with the cord be thus served, violent 
pain immediately follows. 

When no apparent effect follows upon the irritation of 
any nerve, it is not probable that the molecules of the 
nerve remain unchanged. On the contrary, it would ap- 
pear that the same change occurs in all cases ; but a motor 
nerve is connected with nothing that can make that change 
apparent save a muscle : and a sensory nerve with nothing 
that can show an effect but the central nervous system. 

320. Molecular Changes in Irritated Nerves. — It will 
be observed that in all the experiments mentioned there is 
evidence that, when a nerve is irritated, a something, prob- 
ably a change in the arrangement of its molecules, is prop- 
agated along the nerve-fibres. If a motor or a sensory 
nerve be irritated at amy point, contraction in the muscle, 
or sensation in the central organ, immediately follows. But, 
if the nerve be cut, or even tightly tied at any point between 



THE SPIXAL CORD— REFLEX ACTIONS. 293 

the part irritated and the muscle or central organ, the effect 
at once ceases, just as cutting a telegraph-wire stops the 
transmission of the electric current or impulse. When a 
limb, as we say, "goes to sleep," it is because the nerves 
supplying it have been subjected to pressure sufficient to 
destroy the nervous ' continuity of the fibres. We lose 
voluntary control over, and sensation in, the limb, and 
these powers are only gradually restored as that nervous 
continuity returns. 

Having arrived at this notion of an impulse traveling 
along a nerve, we readily pass to the conception of a sen- 
sory nerve as a nerve which, when active, brings an im- 
pulse to the central organ, or is afferent; and of a motor 
nerve, as a nerve which carries away an impulse from the 
organ, or is efferent. It is very convenient to use these 
terms, to denote the two great classes of nerves ; for, as 
we shall find (323), there are afferent nerves which are not 
sensor}' in the sense of -giving rise to a change of con- 
sciousness, or sensation, while there are efferent nerves 
which are not motor, in the sense of inducing muscular 
contraction. Such, for example, are the nerves by which 
the electrical fishes give rise to discharges of electricity 
from peculiar organs to which those nerves are distributed. 
The pneumogastric, when it stops the beat of the heart, 
cannot be called a motor, and yet is then acting as an 
efferent nerve. It will, of course, be understood, as pointed 
out above, that the use of these words does not imply that, 
when a nerve is irritated in the middle of its length, the 
impulses set up by that irritation travel only away from 
the central organ if the nerve be efferent, and towards if it 
!>•* afferent. On the contrary, we have evidence that in 

1 Th-ir "nervous continuity"'— because their physical Continuity is not interrupted 
MS Whole, but only that of the BUDStanoe Which actl B8 a conductor of the nervous 
influence; or. it may be that only the conducting power of a part of that substance ]^ 
interfered with. Imagine a tclr<rraph-eab|e. mad.- of delicate caoutchouc tubes, filled 

with mercury— a iqueese would Interrupt the "electrical continuity" of the cable, 
without destroying it> physical continuity. This analogy may not be exact, but it 
helps to make the nerroaa phenomena intelligible. 



294 ELEMENTARY PHYSIOLOGY. 

both cases the impulses travel both ways. All that is 
meant is this, that the afferent nerve, from the disposition 
of its two ends, in the skin, etc., and in the central organ, 
is of use only when impulses are traveling along it towards 
the central organ, and similarly the efferent nerve is of use 
only when impulses are traveling along it, away from the 
central organ. 

321. Similarity of Afferent and Efferent Nerves. — There 
is no difference in structure, in chemical or in physical 
character, between afferent and efferent nerves. The im- 
pulse which travels along them requires a certain time for 
its propagation, and is vastly slower than many other 
forces — even slow T er than sound. 

322. Properties of the Spinal Cord. — Up to this point 
our experiments have been confined to the nerves. We 
may now test the properties of the spinal cord in a similar 
way. If the cord be cut across (say in the middle of the 
back), the legs and all the parts supplied by nerves which 
come off below the section, will be insensible, and no effort 
of the will can make them move ; while all the parts above 
the section will retain their ordinary powers. When a man 
hurts his back by an accident, the cord is not unfrequently 
so damaged as to be virtually cut in two, and then paralysis 
and insensibility of the lower part of the body ensue. 

If, when the cord is cut across in an animal, the cut 
end of the portion below the division, or away from the 
brain, be irritated, violent movements of all the muscles 
supplied by nerves given off from the lower part of the 
cord take place, but there is no sensation. On the other 
hand, if that part of the cord, which is still connected with 
the brain, or better, if any afferent nerve connected with 
that part of the cord be irritated, great pain ensues, as is 
shown by the movements of the animal, but in these move- 
ments the muscles supplied by nerves coming from the 
spinal cord below the cut take no part ; they remain per- 
fectly quiet. 



THE SPINAL CORD— REFLEX ACTIONS. 295 

323. Reflex Action through the Spinal Cord. — Thus, it 
may be said that, in relation to the brain, the eord is a 
great mixed motor and sensory nerve. But it is also much 
more. For, if the trunk of a spinal nerve be 4 cut through, 

is to sever its connection with the cord, an irritation of 
the skin to which the sensory fibres of that nerve are dis- 
tributed, produces neither motor nor sensory effect. 

But, if the cord be cut through anywhere so as to sever 
its connection with the brain, irritation applied to the skin 
of the parts supplied with sensory nerves from the part of 
the cord below the section, though it gives rise to no sen- 
sation, may produce violent motion of the parts supplied 
with motor nerves from the same part of the cord. 

Thus, in the case supposed above, of a man whose legs 
are paralyzed and insensible from spinal injury, tickling 
the soles of the feet will cause the legs to kick out convul- 
sively. And as a broad fact, it may be said that, so long 
as both roots of the spinal nerves remain connected with 
the cord, irritation of any afferent nerve is competent to 
give rise to excitement of some, or the whole, of the effer- 
ent nerves so connected. 

If the cord be cut across a second time at any distance 
below the first section, the efferent nerves below the second 
rut will no longer be affected by irritation of the afferent 
nerves above it — but only of those below the second sec- 
tion. Or, in other words, in order that an afferent impulse 
may be converted into an efferent one by the spinal cord, 
the afferent nerve must be in uninterrupted material com- 
munication witli the efferent nerve, by means of the sub- 
stance of the spinal cord. 

This peculiar power of the cord, by which it i> com- 
petent to convert afferent into efferent impulses, 18 that 
which distinguishes it physiologically, as a central organ, 

from a nerve, and is called rrffr.r action. It is a power 

possessed by the gray matter, and not by the white sub- 
stance of the cord. 



296 ELEMENTARY PHYSIOLOGY. 

324. Distribution of Reflex Effects. — The number of the 
efferent nerves which may be excited by the reflex action 
of the cord is not regulated alone by the number of the 
afferent nerves which are stimulated by the irritation 
which gives rise to the reflex action. Nor does a simple 
excitation of the afferent nerve by any means necessarily 
imply a corresponding simplicity in the arrangement and 
succession of the reflected motor impulses. Tickling the 
sole of the foot is a very simple excitation of the afferent 
fibres of its nerves ; but, in order to produce the muscular 
actions by which the legs are drawn up, a great multitude 
of efferent fibres must act in regulated combination. In 
fact, in a multitude of cases, a reflex action is to be re- 
garded rather as an order given by an afferent nerve to 
the cord, and executed by it, than as a mere rebound of 
the afferent impulse into the first efferent channels open 
to it. 

The various characters of these reflex actions may be 
very conveniently studied in the frog. If a frog be decapi- 
tated, or, better still, if the spinal cord be divided close 
to the head and the brain be destroyed by passing a blunt 
w^ire into the cavity of the skull, the animal is thus de- 
prived (by an operation which, being almost instantaneous, 
can give rise to very little pain) of all consciousness and 
volition, and yet the spinal cord is left intact. At first the 
animal is quite flaccid and apparently dead, no movement 
of any part of the body (except the beating of the heart) 
being visible. This condition, how T ever, being the result 
merely of the so-called shock of the operation, very soon 
passes off, and then the following facts may be observed : 

So long; as the animal is untouched, so I0112: as no 
stimulus is brought to bear upon it, no movement of any 
kind takes place — volition is wholly absent. 

If, however, one of the toes be gently pinched, the leg 
is immediately drawn up close to the body. 

If the skin between the thighs around the anus be 



THE SPINAL CORD— REFLEX ACTIONS. 29 7 

pinched, the legs are suddenly drawn up and thrust out 
again violently. 

If the flank be very gently stroked, there is simply a 
twitching movement of the muscles underneath ; if it be 

more roughly touched, or pinched, these twitching move- 
ments become more general along the whole side of the 
creature, and extend to the other side, to the hind-legs, 
and even to the front-legs. 

If the digits of the front-limbs be touched, these will be 
drawn close under the body as in the act of clasping. 

If a drop of vinegar or any acid be placed on the top 
of one thigh, rapid and active movements will take place 
in the leg. The foot will be seen distinctly trying to rub 
off the drop of acid from the thigh. And, what is still 
more striking, if the leg be held tight and so prevented 
from moving, the other leg- will beo-in to rub off the acid. 
Sometimes, if the drop be too large or too strong, both legs 
begin at once, and then frequently the movements spread 
from the legs all over the body, and the whole animal is 
thrown into convulsions. 

Now, all these various movements, even the feeblest and 
simplest, require a certain combination of muscles, and 
some of them, such as the act of rubbing off the acids, are 
in the highest degree complex. In all of them, too, a cer- 
tain purpose or end is evident, which is generally either to 
remove the body or part of the body from the stimulus, 
from the cause of irritation, or to thrust away the offending 
object from the body: in the more complex movements 
such a purpose is strikingly apparent. 

It seems, in bet, thai in the frog's spinal cord there are 

- of nervous machinery desl ined to be used for a variety 
of movements, and thai a stimulus passing along a Bensory 
nerve to the cord sets one or the other of these pieces of 
machinery at work. 

325. The Spinal Cord as a Conductor. — Thus the spinal 
cord is, in part, merely a transmitter of impulses to and 



298 ELEMENTARY PHYSIOLOGY. 

from the brain ; but, in part, it is an independent nervous 
centre, capable of originating combined movements upon 
the reception of the impulse of an afferent nerve. 

Regarding it merely as a conductor, the question arises, 
Do all parts of it conduct all kinds of impulses indiffer- 
ently ? or, are certain kinds of impulses communicated only 
through particular parts of the cord ? 

The following experiments furnish a partial reply to 
these questions : 

If the anterior half of the white matter of the dorsal 
part of the cord be cut through, the will is no longer capa- 
ble of exerting any influence on the muscles which are sup- 
plied with nerves from the lower segment of the cord. A 
similar section, carried through the posterior half of the 
white matter in this region, has no effect on the transmis- 
sion of voluntary impulses. It is obvious, therefore, that. 
in the dorsal part of the cord, nervous impulses from the 
brain are sent through the anterior part of the white matter. 

326. Conduction of the Gray Matter. — The posterior 
half of the white matter may be cut through at one point, 
and the anterior half at a point a little higher up, so that 
all the white fibres shall be divided transversely by the 
one cut or the other, without any interference with the ma- 
terial continuity of the cord, or damage to the gray matter. 

When this has been done, irritation of those sensory 
nerves which are connected with parts below the section 
excites the sensation of pain as strongly as ever. Hence 
it follows that the afferent impulses, which excite pain 
when they reach the brain, pass through, and are conveyed 
by, the gray matter. And it has been found, by experi- 
ment, that, so long as even a small portion of the gray 
matter remains entire, these afferent impulses are efficiently 
transmitted. Singularly enough, however, irritation of the 
gray matter itself is said not to cause pain. 1 

1 This is why, in the experiment described at end of Chapter II., it is better, for test- 
ing- the presence of sensations, to irritate afferent nerves connected with the cord rather 
than the cut end of the cord itself. 



THE BRAIN. 299 

If one-half of the cord, say the right, be cut through, 
transversely, down to its very middle, so as to interrupt all 
continuity of both white and gray matter between its upper 
and lower parts, irritation of the skin of the right side of 
the body, below the line of section, will give rise to as 
much pain as before, but all voluntary power will be lost 
in those muscles of that side, which are supplied by nerves 
coming off from the lower portion of the cord. Hence it 
follows, that the channels by which the afferent impulses 
are conveyed must cross over from the side of the cord 
which they enter to the opposite side ; while the efferent 
impulses, sent down from the brain, must travel along that 
side of the cord by which they pass out. 

If this be true, it is clear that a longitudinal section, 
t a ven through the exact middle of the cord, will greatly 
impair, if not destroy, th,e sensibility of both sides of the 
body below the section, but will leave the muscles under 
the control of the will. . And it is found experimentally 
that such is verv largely the case. 

Section II. — The Brain. 

327. The Vaso-motor Centres. — Such are the functions 
of the spinal cord, taken as a whole. The spinal nerves 
are, as we have said, chiefly distributed to the muscles and 
to the skin. The nerves of the blood-vessels, for instance, 
the so-called vaso-motor nerves (65), belong not to the 
spinal, but to the sympathetic system. Along the spinal 
column, however, the spinal nerves give off branches which 
run in and join the sympathetic system. And it appears 
that many at least of the fibres which run along in the 
sympathetic nerves going to blood-vessels, do really spring 
from the spinal cord, finding their way into the sympa- 
thetic system through these communicating or commissural 
branch 

Experiments, moreover, go to show thai the nervous in- 
fluence which keeps up the tone of the blood-vessels, that 



300 



"elementary physiology. 




Fig. 103. 



The Base of the Brain. 



A, frontal lobe; B. temporal lobe of the cerebral hemispheres; Ob. cerebellum; /., 
the olfactory nerve; II.. the optic nerve ; III. IV., VI, the nerves of the muscles of 
the eye; F., the trigeminal nerve; VII, the portio dura ; VIII, the auditory nerve 
IX., the glossopharyngeal ; X., the pneumogastric : .IV.. the spinal accessory; XII., 
the hypoglossal, or" motor nerve of the tongue. The number VI. is placed upon the 
pons Varolii. The crura cerebri are the broad bundles of fibres which lie between 
the third and the fourth nerves on each side. The medulla oblongata (J/) is seen to 
be really a continuation of the spinal cord ; on the lower end are seen the two cres- 
cents of gray matter; the section, in fact, has been carried through the spinal cord, a 
little below "the proper medulla oblongata. From the sides of the medulla oblongata 
are seen coming off the X., XL, and XII. nerves ; and just where the medulla is cov 
ered, so to speak, by the transversely disposed pons Varolii, are seen coming off the 
VII. nerve, and more towards the middle line the TV. Out of the substance of the 
pons springs the V. nerve. In front of that is seen the well-defined anterior border 
of the pons ; and coming forward in front of that line, between the IV. and III nerves, 
on either side, are seen the crura cerebri. The two round bodies in the angle between 
the diverging crura are the so-called corpora albicantia. and in front of them is P, 
the pituitary body. This rests on the chiasma, or junction, of the optic nerves ; the 
continuation of each nerve is seen sweeping round the crura cerebri on either side. 
Immediately in front, between the separated frontal lobes of the cerebral hemispheres, 
is seen the corpus callosum, CC. The fissure of Sylvius, about on a level with /. on 
the left and II. on the right side, marks the division between frontal and temporal 
lobes. 



THE BRAIN. 301 

is, which keeps them in the usual condition of moderate 
contraction, proceeds from the spinal cord. 

The cord is, therefore, spoken of as containing centres 
for the vasomotor nerves, or, more shortly, vaso- motor 
a ntres. 

For example, the muscular Avails of the blood-vessels 
supplying the ear and the skin of the head generally, are 
made to contract, as has been already mentioned, by ner- 
vous fibres derived immediately from the sympathetic. 
These fibres, however, do not arise from the sympathetic 
ganglia, but simply pass through them on their way from 
the spinal cord to the upper dorsal region of which they 
can all be traced. At least, this is the conclusion drawn 
from the facts, that irritation of this region of the cord 
produces the same effect as irritation of the vaso -motor 
nerves themselves, and that destruction of this part of the 
cord paralyzes them. 

Recent researches, however, have shown that the ner- 
vous influence does not originate here, but proceeds from 
higher up, from the medulla oblongata in fact, and simply 
passes down through this part of the spinal cord on its 
way to join the sympathetic ganglia. 

328. Outlines of Anatomy of the Brain, — The brain 
(Fig. 103) is a complex organ, consisting of several parts, 
the hindermost of which, termed medulla oblongata, passes 
insensibly into, and in its lower part has the same struct- 
ure as, the spinal cord. 

Above, however, it widens out, and the central canal, 
spreading with it, becomes a broad cavity, which (leaving 
certain anatomical minutiae aside) may be said to be widely 

': above. This cavity is termed the fourth ventricle. 
Overhanging the fourth ventricle is a great laminated mass, 
the cen helium ( CT., Pigs. 103, 1<>4. 105). On each side, this 
organ Bends down several layers oftransvt rse fibres, which 
•]> across tin- brain and meel in the middle line of it > 
base, forming a kind of bridge (called pons Varolii^ Fig. 



302 



ELEMENTARY PHYSIOLOGY. 



103), in front of the medulla oblongata. The longitudinal 
nerve-fibres of the medulla oblongata pass forwards, among, 
and between these layers of transverse fibres, and become 
visible, in front of the pons, as two broad diverging bun- 
dles, called crura cerebri (Fig. 103). Above the crura cere- 




FlCr. 104. 

A side-view of the brain and upper part of the spinal cord in place— the parts which 
cover the cerebro- spinal centres being removed. C. C. the convoluted surface of the 
right cerebral hemisphere; (76., the cerebellum; 31. Ob., the medulla oblongata; B.< 
the bodies of the cervical vertebrae ; Sp., their spines ; JV., the spinal cord with the 
spinal nerves. 



bri lies a mass of nervous matter raised up into four hemi- 
spherical elevations, called corpora quadrigemina (C.Q., 
Fig. 105). Between these and the crura cerebri is a nar- 



THE BRAIN. 303 

row passage, which leads from the fourth ventricle into 
what is termed the third ventricle of the brain. The third 
ventricle is a narrow cavity lodged between two great 
masses of nervous matter, called optic thahoni, into which 
the crura cerebri pass. The roof of the third ventricle is 
merely membranous ; and a peculiar body of unknown 
function, the pineal body, is connected with it. The floor 
of the third ventricle is produced into a sort of funnel, 
which ends in another anomalous organ, the pituitary body 
{Ft., Fig. 105; P, Fig. 103). 

The third ventricle is closed, in front, by a thin layer 
of nervous matter ; but, beyond this, on each side, there 
is an aperture in the boundary wall of the third ventricle 
which leads into a large cavity. The latter occupies the 
centre of the cerebral hemisphere, and is called the lateral 
ventricle. Each hemisphere is enlarged backwards, down- 
wards, and forwards, into as many lobes / and the lateral 
ventricle presents corresponding prolongations, or cornua. 

The floor of the lateral ventricle is formed by a mass 
of nervous matter called the corpus striatum, into which 
the fibres that have traversed the optic thalamus enter 
(Fig. 105, C.S.). 

The hemispheres are so large that they overlap all the 
other parts of the brain, and, in the upper view, hide them. 

Their applied faces are separated by a medium fissure 
for the greater part of their extent; but, inferiorly, are 
joined by a thick mass of transverse fibres, the corpus ccd- 
losum (Fig. 103, (7.(7.). 

The outer surfaces of the hemispheres are marked out 
into convolutions^ or f/yri,by numerous deep fissures (or 
iulct), into which the pia mater enters. One large and 
deep fissure, which separates the anterior from the middle 
division of the hemisphere is called the fissure of Sylvius 
(Fig. 103). 

329. Arrangement of the White and Gray Matter. — In 
thr me /'///'/ oblongata the arrangement of the white and 



304 ELEMENTARY PHYSIOLOGY. 

gray matter is substantially similar to that which oltains 
in the spinal cord ; that is to sa} T , the white matter is ex- 
ternal and the gray internal. But, in the cerebellum and 
cerebral hemispheres, the gray matter is external and the 
white internal ; while, in the optic thalami and corpora 
striata, gray matter and white matter are variously inter- 
mixed. 

Section III. — The Cerebral Nerves. 

330. Their Distribution. — Nerves are given off from 
the brain in pairs, which succeed one another from before 
backwards, to the number of twelve (Fig. 105). 

The first pair, counting from before backwards, are the 
olfactory nerves, and the second are the optic nerves. The 
functions of these have already been described. 

The third pair are called motores oculi (movers of the 
eye), because they are distributed to all the muscles of the 
eye except two. 

The nerves of the fourth pair and of the sixth pair 
supply each one of the muscles of the eye, on each side ; 
the fourth going to the superior oblique muscle, and the 
sixth to the external rectus. Thus the muscles of the eye, 
small and close together as they are, receive their nervous 
stimulus by three distinct nerves. 

Each nerve of the fifth pair is very large. It has two 
roots, a motor and a sensory, and further resembles a 
spinal nerve in having a ganglion on its sensory root. It 
is the nerve which supplies the skin of the face and the 
muscles of the jaws, and, having three chief divisions, is 
often called trigeminal. One branch, containing sensory 
fibres, supplies the front of the tongue, and is often spoken 
of as the gustatory. 

The seventh pair furnish with motor nerves the muscles 
of the face, and some other muscles, and are called facial. 

The eighth pair are the auditory nerves. As the sev- 
enth and eighth pairs of nerves leave the cavity of the 
skull together, they are often, and especially by English 



THE CEREBRAL NERVES. 



305 



writers on anatomy, reckoned as one, divided into portio 
dura, or hard part (the facial); and portio mollis, or soft 
part (the auditory) of the " seventh " pair. 

The ninth pair in order, the glossopharyngeal, are 
mixed nerves ; each being*, partly, a nerve of taste, and 
supplying the back of the tongue, and, partly, a motor 
nerve for the pharyngeal muscles. 




Fig. 105. 

A Diagram illistrating the Arrangement of the Parts of the Brain and 

the Origin of the Nerves. 

//.. the cerebral hemispheres; C.S., corpus striatum; Th., optic thalamus; P., 
pineal body: P/., pituitary body; C.Q., corpora quadri<remina; Cb., cerebellum; 3/, 
medulla oblongata: I.— XII., the pairs of cerebral nerves; Sp. 1, Sp. '2, the first and 
second pairs of spinal nerves. 



The tenth pair is formed by the two pnewno gastric 
nerves, often called the par vagum. These very impor- 
tant nerves, and the next pair, are the only cerebral nerves 
which arc distributed to regions of the body remote from 
the head Tin; pneumogastric supplies the larynx, the 
lungs, the liver, and the stomach, and branches of it are 
connected with the heart. 

The eli venth pair^ again, culled spinal accessory, differ 
widely from all the rest, in arising from the sides of the 
20 



306 ELEMENTARY PHYSIOLOGY. 

spinal marrow, between the anterior and posterior roots of 
the dorsal nerves. They run up, gathering fibres as they 
go, to the medulla oblongata, and then leave the skull by 
the same aperture as the prieumogastric and glossopha- 
ryngeal. They are purely motor nerves, supplying certain 
muscles of the neck, while the pneumogastric is mainly 
sensory, or at least afferent. As, on each side, the glosso- 
pharyngeal, pneumogastric, and spinal accessory nerves, 
leave the skull together, they are frequently reckoned as 
one pair, which is then counted as the eighth. 

The last two nerves, by this method of counting, be- 
come the ninth pair, but they are really the twelfth. They 
are the motor nerves which supply the muscles of the 
tongue. 

331. Olfactory and Optic Nerves. — Of these nerves, the 
two foremost pair do not properly deserve that name, but 
are really processes of the brain. The olfactory pair are 
prolongations of the cerebral hemispheres ; the optic pair, 
of the walls of the third ventricle ; and it is worthy of re- 
mark, that it is only these two pair of what may be called 
false nerves which arise from any part of the brain but 
the medulla oblongata — all the other true nerves being 
indirectly, or directly, traceable to that part of the brain, 
while the olfactory and optic nerves are not so traceable. 

332. Effects of Injuries to the Medulla Oblongata. — As 
might be expected from this circumstance alone, the me- 
dulla oblongata is an extremely important part of the 
cerebro-spinal axis, injury to it giving rise to immediate 
evil consequences of the most serious kind. 

Simple puncture of one side of the floor of the fourth 
ventricle produces for a while an increase of the quantity 
of sugar in the blood, beyond that which can be destroyed 
in the organism. The sugar passes off by the kidneys, 
and thus this slight injury to the medulla produces a 
temporary disorder closely resembling the disease called 
diabetes. 



THE CEREBRAL NERVES. 307 

More extensive injury arrests the respiratory processes, 
the medulla oblongata being the nervous centre which 
gives rise to the contractions of the respiratory muscles 
and keeps the respiratory pump at work. 

The motor nerves engaged in ordinary respiration are 
certain spinal nerves, viz., the intercostal nerves supplying 
the intercostal muscles, and the phrenic nerve supplying 
the diaphragm. These motor nerves are undoubtedly 
brought into action by impulses proceeding at intervals 
from the medulla oblongata. But how these rhythmic 
impulses originate in the medulla oblongata is not very 
clear. There are reasons for thinking that the presence 
of venous blood in the lungs acts as a stimulus to the end- 
ings of the pneumogastric nerves, and sets going impulses 
which, traveling up along those nerves to the medulla 
oblongata, there produce respiratory movements by reflex 
action. But this is not all, for respiration, though pro- 
foundly modified, is not arrested by division or destruction 
of the pneumogastric nerves. Probably the medulla ob- 
longata contains a nervous mechanism which acts as an 
independent centre in a manner somewhat similar to the 
ganglia of the heart ; and so goes on of itself, though ex- 
tremely sensitive to, and thus continually influenced by, 
the rendition of the blood not only in the lungs but all 
over l he body. 

If the injuries to the medulla oblongata be of such a 
kind ms to irritate the roots of the pneumogastric nerve 
violently, death supervenes by the stoppage of the heart's 
aet inn in the manner already described. (See 69.) 

333. Crossing of Impulses in the Medulla.— The affer- 
ent impulses, which are transmitted through the cord to 
the brain and awake sensation there, cross, as we have 

,. from one half of the cord te the other, immediately 
after thev enter it by the posterior root- of the spinal 
nerves : while the efferent, or volitional, impulses from the 
brain remain, throughout the cord, in that hall' of it from 



308 ELEMENTARY PHYSIOLOGY. 

which they will eventually pass by the anterior roots. But, 
at the lower and front part of the medulla oblongata, these 
also cross over ; and the white fibres which convey them 
are seen passing obliquely from left to right and from 
right to left in what is called the decussation of the ante- 
rior pyramids (Fig. 103). Hence, any injury, at a point 
higher up than the decussation, to the nerve-fibres which 
convey motor impulses from the brain, paralyzes the mus- 
cles of the body and limbs of the opposite side. 

Division, therefore, of one of the crura cerebri, say the 
right, gives rise to paralysis of the left side of the body and 
limbs, and the animal operated upon falls over to the left 
side, because the limbs of that side are no longer able to 
support the weight. 

But, as the motor nerves given off from the brain itself 
and arising from the medulla above the decussation of the 
pyramids do not cross over in this way, it follows, that 
disease or injury at a given point, on one side of the me- 
dulla oblongata, involving at once the course of the voli- 
tional motor channels to the spinal marrow, and the origins 
of the cranial motor nerves, will affect the same side of the 
head as that of the injury, but the opposite side of the 
body. . 

If the origin of the left facial nerve, for example, be 
injured, and the volitional motor fibres going to the cord 
destroyed, in the upper part of the medulla oblongata, the 
muscles of the face of the left side will be paralyzed, and 
the features will be drawn over to the opposite side, the 
muscles of the right side having nothing to counteract 
their action. But it is the right arm, and the right leg 
and side of the body, which will be powerless. 

Section IV. — Unconscious Cerebration, 

334. Seat of Intelligence and Will. — The functions of 
most of the parts of the brain which lie in front of the 
medulla oblongata are, at present, very ill understood ; but 



UNCONSCIOUS CEREBRATION. 309 

it is certain that extensive injury, or removal, of the cere- 
bral hemispheres puts an end to intelligence and voluntary 
movement, and leaves the animal in the condition of a 
machine, working by the reflex action of the remainder of 
the cerebro-spinal axis. 

We have seen that in the frog the movements of the 
body which the spinal cord alone, in the absence of the 
whole of the brain including the medulla oblongata, is 
capable of executing, are of themselves strikingly complex 
and varied. But none of these movements are voluntary 
or spontaneous ; they never occur unless the animal be 
stimulated. Removal of the cerebral hemispheres is alone 
sufficient to deprive the frog of all spontaneous or voluntary 
movements ; but the presence of the medulla oblongata 
and other parts of the brain (such as the corpora quadri- 
gemina, or what corresponds to them in the frog, and the 
cerebellum) renders the animal master of movements of a 
far higher nature than when the spinal cord only is left. 
In the latter case the animal does not breathe when left to 
itself, lies flat on the table with its fore-limbs beneath it in 
an unnatural position ; when irritated kicks out its legs, 
and may be thrown into actual convulsions, but never 
jumps from place to place ; when thrown into a basin of 
water falls to the bottom like a lump of lead, and when 
placed on its back will remain so, without making any 
effort to turn over. In the former case the animal sits on 
tin 1 table, resting on its front-limbs, in the position natural 
t<> a frog; breathes quite naturally; when pricked behind 
jumps away, often getting over quite a considerable dis- 
tance; when thrown into water begins at once to swim, 
and continues swimming until it finds some object on 
which it can rest ; nud when placed on its bade immedi- 
ately turns over and resumes its natural position. Not 
only so. but the following very striking experiment may 
be performed with it : Placed on a small board it remains 
perfectly motionless so long as the board is horizontal; if, 



310 ELEMENTARY PHYSIOLOGY. 

however, the board be gradually tilted up so as to raise 
the animal's head, directly the board becomes inclined at 
such an angle as to throw the frog's centre of gravity too 
much backwards, the creature begins slowly to creep up 
the board, and, if the board continues to be inclined, will 
at last reach the edge, upon which when the board be- 
comes vertical he will seat himself with apparent great 
content. Nevertheless, though liis movements when they 
do occur are extremely well combined and apparently 
identical with those of a frog possessing the whole of his 
brain, he never moves spontaneously, and never stirs un- 
less irritated. 

There can be no doubt that the cerebral hemispheres 
are the seat of powers essential to the production of those 
phenomena which we term intelligence and will ; but there 
is no satisfactory proof, at present, that the manifestation 
of any particular kind of mental faculty is especially allot- 
ted to, or connected with, the activity of any particular 
region of the cerebral hemispheres. 

335. Reflex Action of the Brain. — Even while the cere- 
bral hemispheres are entire, and in full possession of their 
powers, the brain gives rise to actions which are as com- 
pletely reflex as those of the spinal cord. 

When the eyelids wink at a flash of light, or a threatened 
blow, a reflex action takes place, in which the afferent 
nerves are the optic, the efferent the facial. When a bad 
smell causes a grimace, there is a reflex action through 
the same motor nerve, while the olfactory nerves constitute 
the afferent channels. In these cases, therefore, reflex 
action must be effected through the brain, all the nerves 
involved being cerebral. 

When the whole body starts at a loud noise, the affer- 
ent auditory nerve gives rise to an impulse which passes 
to, the medulla oblongata, and thence affects the great 
majority of the motor nerves of the body. 

336. Reflex Actions in reading aloud, — It may be said 



UNCONSCIOUS CEREBRATION. 311 

that these are mere mechanical actions, and have nothing 
to do with the operations which we associate with intelli- 
gence. But let us consider what takes place in such an 
act as reading aloud. In this case, the whole attention of 
the mind is, or ought to be, bent upon the subject-matter 
of the book; while a multitude of most delicate muscular 
actions are going on, of which the reader is not in the 
slightest degree aware. Thus the book is held in the 
hand, at the right distance from the eyes ; the eves are 
moved from side to side, over the Hues and up and down 
the pages. Further, the most delicately - adjusted and 
rapid movements of the muscles of the lips, tongue, and 
throat, of the laryngeal and respiratory muscles, are in- 
volved in the production of speech. Perhaps the reader 
is standing up and accompanying the lecture with appro- 
priate gestures. And yet every one of these muscular acts 
may be performed with utter unconsciousness, on his part, 
of any thing but the sense of the words in the book. In 
other words, they are reflex acts. 

337. Artificial Reflex Actions— Education. — The reflex 
actions proper to the spinal cord itself are natural, and are 
involved in the structure of the cord and the properties of 
its constituents. By the help of the brain we may acquire 
an infinity of artificial reflex actions ; that is to say, an ac- 
tion may require all our attention and all our volition for 
its first, or second, or third performance, but by frequent 
repetition it becomes, in a manner, part of our organiza- 
tion, and is performed without volition, or even conscious- 
ness. 

A- every one knows, it takes a soldier a long time to 
Irani his drill — for instance, to put himself into the attitude 
of "attention" at the instant the word of command ia 
heard. But. after ;> time, the sound of the wool gives rise 
to the act, whether the soldier be thinking of it or not. 

There is a >tor\\ which is credible enough, though it mav 

not be true, of a practical joker, who. seeing a discharged 



312 ELEMENTARY PHYSIOLOGY. 

veteran carrying home his dinner, suddenly called out " At- 
tention ! " whereupon the man instantly brought his hands 
down, and lost his mutton and potatoes in the gutter. The 
drill had been thorough, and its effects had become embodied 
in the man's nervous structure. 

The possibility of all education (of which military drill 
is only one particular form) is based upon the existence 
of this power which the nervous system possesses, of or- 
ganizing conscious actions into more or less unconscious, 
or reflex, operations. It may be laid down as a rule that, 
if any two mental states be called up together, or in suc- 
cession, with due frequency and vividness, the subsequent 
production of the one of them will suffice to call up the 
other, and that whether we desire it or not. 

The object of intellectual education is to create such 
indissoluble associations of our ideas of things, in the order 
and relation in which they occur in Nature ; that of a moral 
education is to unite as fixedly, the ideas of evil deeds with 
those of pain and degradation, and of good actions with 
those of pleasure and nobleness. 

338. The Sympathetic System. — The sympathetic sys- 
tem consists chiefly of a double chain of ganglia, lying at 
the sides and in front of the spinal column, and connected 
with one another, and with the spinal nerves, by commis- 
sural cords. From these ganglia, nerves are given off 
which for the most part follow the distribution of the ves- 
sels, but which, in the thorax and abdomen, form great 
net-works, or plexuses, upon the heart and about the stom- 
ach. It is probable that a great proportion of the fibres 
of the sympathetic system is derived from the spinal cord ; 
but others also, in all probability, originate in the ganglia 
of the sympathetic itself. The sympathetic nerves influ- 
ence the muscles of the vessels generally, and those of the 
heart, of the intestines, and of some other viscera : and it 
is probable that their ganglia are centres of reflex action 
to afferent nerves from these organs. But many of the 



DERMAL TISSUES. 313 

motor nerves of the vessels are, as we have seen, under the 
influence of particular parts of the spinal cord, though they 
pass through sympathetic ganglia. 



CHAPTER XII. 
histology; or, the minute structure of the tissues. 

Section I. — Dermal Tissues. 

339. The Microscopical Analysis of the Body. — The 

various organs and parts of the body, the working of which 
has now been described, are not merely separable by the 
eye and the knife of the anatomist into membranes, nerves, 
muscles, bones, cartilages, and so forth ; but each of them 
is, by the help of the microscope, susceptible of a finer 
analysis, into certain minute constituents which, for the 
present, may be considered the ultimate structural ele- 
ments of the body. 

340. Nuclei and Cells. — There is a time when the human 
body, or rather its rudiment, is of one structure throughout, 
consisting of a more or less transparent matrix, very simi- 
lar in nature to the substance of which the white blood- 
corpuscles are composed, and often called protoplasm, 
through which are scattered minute rounded particles of a 
different optical aspect. These particles are called niich i ; 
and as the matrix, or matter in which these nuclei are em- 
bedded, readily breaks up into spheroidal masses, one for 
each nucleus, and these investing masses easily take on the 
form of tresiclfea or cells, this primitive structure is called 
eMylar, and cadi re]] is said to be in<<-1<<t1< <K 

Tin- material of the body when in this stage of growth 
is often spoken of as indifferent tissue. \ very fair idea 

of its nature may he formed by supposing a multitude of 



314 



ELEMENTARY PHYSIOLOGY. 



white blood- corpuscles to be collected together into a soft 
but yet semi-solid mass. 

In the present use of the term any distinct mass of pro- 
toplasm or living material may be called a cell. In the 
vast majority of cases, however, the cell contains a nucleus, 
distinguished, as has just been said, from the cell-substance 
in which it lies. Very frequently, but by no means always, 
the outer layer of the cell-substance is hardened into a dis- 
tinct casing or envelope, the cell-wall, the cell then becom- 
ing an undeniable vesicle, and the cell-substance being often 
spoken of as the cell-contents. The cell-substance may re- 
main as soft semi-solid protoplasm, or may be hardened in 
various ways, or may be wholly or partially liquefied ; in 
the latter case a cell-wall is naturally always present. 







Fig. 106. 

A, vertical section of a layer of epidermis, or epithelium, from its free to its deep 
surface. B, lateral views of the cells of which this layer is composed at different 
heights; a, cell in the deepest layer, and therefore most recently formed and least 
altered; &, cell higher up, and therefore somewhat changed; c, cZ, cells still more 
changed, and much flattened. C, scales such as d viewed from their flat side. (Mag- 
nified about two hundred and fifty diameters.) 

As development goes on, the nuclei simply increase in 
number by division and subdivision, without undergoing 



DERMAL TISSUES. 315 

any marked change; ' but the substance in which they are 
embedded becomes very variously modified, both chemi- 
cally and structurally, and gives rise to those peculiarities 
by which completely formed tissues are distinguished from 
one another. 

341. Epidermis and Epithelium. — In the adult body the 
simplest forms of tissue, i. e., those in which the matrix 
lias been least changed, are perhaps the various kinds of 
epithelium (including the epidermis). 

These are distinctly cellular in nature — that is, the pcr- 
tion of the matrix belonging to each nucleus can, with a 
little pains, be recognized as distinct from the portions 
belonging to the other nuclei. In fact, they differ from 
white blood-corpuscles chiefly in two points : firstly, the 
matrix of each cell becomes more or less chemically changed 
BO as to lose its soft protoplasmic nature (and, at the same 
time, its power of executing amoeboid movements) ; and, 
secondly, takes on a rigid definite form, which may or may 
not be globular. These epithelial tissues are constantly 
growing in their deepest parts, and are, as constantly, be- 
ing shed at their surfaces. 

The deep part consists of a layer of such globular, 
nucleated cells as have been mentioned, the number of 
which is constantly increasing by the spontaneous division 
of the nuclei and cells. The increase in number thus ef- 
fected causes a thrusting of the excess of cell-population 
towards the surface; on their way to which they become 
flattened, and their walls acquire a horny texture. Arrived 
at the surface, they are mere dead horny scales, and are 
thrown off (Fig. 10')). 

Epithelium of the kind just described is called squa- 
mous. It is found in the mouth, and its scales may always 
1).- obtained in abundance by scraping the inside of the lip. 

v -. nncleoj dhideeinto two. aa<l each half toon growl up into the hz<- of the 
\t nucleus. While tide ii going on, tin- matrla round th • nuclei alio divides, each 

til: :i quantity of matrix allotted to it. bo u to brio a new <•« ii exactly 
like the oM on*.-, from which 



316 



ELEMENTARY PHYSIOLOGY. 



Epidermis consists of exactly similar cells, except that 
the conversion of the topmost cells into horny scales is 
still more complete. The nucleus, too, is eventually lost. 
The deep layers of epidermis, consisting of softer cells not 
yet flattened or made horny, often form quite a distinct 
part, and these are often spoken of as the rete mucosum. 
(See Fig. 40, b; Fig. 110, d). 

In other parts of the alimentary tract, as in the intes- 
tines, the full-grown epithelial cells are placed side by side 




Fro. 107. 

Ciliated Epithelium. 

a, the submucous vascular tissue; !>, the deep layer of young epithelium-cells; c, 
the cylindrical full-grown cells, with (d) the cilia, (Magnified about three hundred 
and fifty diameters.) 

with one another, and perpendicular to the surface of the 
membrane. Such epithelium is called cylindrical (Fig. 
55, J, 6'), or columnar. 

In some places, such as in the gastric glands, in some 
parts of the kidney, in the ureters and elsewhere, the epi- 
thelial cells remain globular or spheroidal. 

Squamous epithelium generally consists of many layers 
of cells, one over the other ; in other forms of epithelium 
there are few, in some cases apparently only two, layers. 

Ciliated epithelium is usually of the cylindrical kind, 
and differs from other epithelium only in the circumstance 
that one or more incessantly vibrating filaments are devel- 
oped from the free surface of each cell. (See 196.) 



DERMAL TISSUES. 



317 



342. Nails. — In certain regions of the integument, the 
epidermis becomes metamorphosed into nails and hairs. 

Underneath each nail the deep or dermic layer of the 
integument is peculiarly modified to form the bed of the 








Fiu. 108.— A longitudinal and vertical section of a nail: a. the fold at the base of 
Oh nail : h. the- nail; r. the he 1 of the nail. 

Fig. I" 1 .* is a trans' n of the same: a. a small lateral fold of the into<rn- 

rnrnr : } >. nail: c bed of tin- nail with if- ridges. 

FL-. 11' ' i- a highly- magnified view of a part of the foregoing: c, the ridges; oT, the 
- of epidermis; <■. the horny scales coalesced into nail-substance. 

■ r four diameters ; Pig. 110 magnified about two 

; . It is very vascular, and raised up into numerous 
parallel ridges, like elongated papillae (Figs, 109, 110). 
The* surfaces of all these are covered with growing epider- 
mic cells, whirl), as they flatten and become converted into 



318 ELEMENTARY* PHYSIOLOGY. 

horn, coalesce into a solid continuous plate, the nail. At 
the hinder part of the bed of the nail, the integument forms 
a deep fold, from the bottom of which, in like manner, new 
epidermic cells are added to the base of the nail, which is 
thus constrained to move forward. 

The nail, thus constantly receiving additions from be* 
low and from behind, slides forwards over its bed, and pro- 
jects beyond the end of the finger, where it is worn awa}^, 
or cut off. 

343. Hairs, — A hair, like a nail, is composed of coa- 
lesced horny cells ; but, instead of being only partially sunk 
in a fold of the integument, it is at first wholly inclosed in 
a kind of bag, the hair-sac, from the bottom of which a 
papilla (Fig. Ill, i\ which answers to a single ridge of the 
nail, arises. The hair is developed by the conversion into 
horn, and coalescence into a shaft, of the superficial epi- 
dermic cells coating the papilla. These coalesced and 
cornified cells being continually replaced by new growths 
from below, which undergo the same metamorphosis, the 
shaft of the hair is thrust out until it attains the full length 
natural to it. Its base then ceases to grow, and the old 
papilla and sac die away, but not before a new sac and pa- 
pilla have been formed by budding from the sides of the 
old one. These give rke to a new hair. The shaft of a 
hair of the head consists of a central pith, or medullary 
matter, of a loose and open texture, which sometimes con- 
tains air; of a cortical substance surrounding this, made 
up of coalesced elongated horny cells; and of an outer 
cuticle, composed of flat horny plates, arranged transversely 
round the shaft, so as to overlap one another by their outer 
edges, like closely-packed tiles. The superficial epidermic 
cells of the hair-sac also coalesce by their edges, and be- 
come converted into root-sheaths, which embrace the root 
of the hair, and usually come away with it, when it is 
plucked out. 

Two sebaceous glands commonly open into the hair-sac 



DERMAL TISSUES. 



310 



near its opening, and supply the hair with a kind of natural 
pomatum; and delicate unstriped muscular fibres are so 
connected with the b air-sac as to cause it to pass from its 
ordinary oblique position into one perpendicular to the 
skin, when they contract (Fig. 39). 

They are made to contract by the influence of cold and 





Fig. 111. 

A B \ir. i\ m II \ir. 

.ft of hair ll <»f tli.- shaft, the mrdnlla not 

beini; \ - wing on the papilla (I) ; a, cuticle of huh ■, 

dermis (and r<><>- I the balr-sac corresponding to 

tween derail -* u i < 1 epidermis; A. derafa <»t 

hair-sac f<.rr- .:u<nt</>: X\ motlthl "t MbaceOUl trlaii'ls; 

». homy epi 



320 



ELEMENTARY PHYSIOLO&X 



terror, which thus give rise to ^horripilation," or " goose- 
skin," and the " standing of the hair on end." 




Fig. 112. 

Part of the shaft of a hair inclosed within its root-sheaths and treated with caustic 
soda, which has caused the shaft to become distorted: <i. medulla; l>. cortical sub- 
stance ; c, cuticle of the shaft ; from d to /. the root-sheaths, in section. (Magnified 
about two hundred diameters.) 

Section II. —Interior Tissues, 

344. The Crystalline Lens. — The crystalline lens is com- 
posed of fibres, which are the modified cells of the epider- 
mis of that inverted portion of the integument from which 
the whole anterior chamber of the eye and the lens are 
primitively formed. 

345. Cartilage. — While epithelium and epidermis are 
found only on the free surfaces of the organs, gristle, or 
cartilage, is a deep-seated structure (see 210, 211). Like 
them it is essentially cellular in nature, but differs from 
them widely in appearance on account of the development 
of a large quantity of the so-called intercellular substance. 
That is to say, the several cells do not lie closely packed 
together and touching each other, but are separated from 
each other by a quantity of material of a different nature 
from themselves. Just as in indifferent tissue each nucleus 
is embedded in a matrix of protoplasm, so in cartilage, 
each cell, i. e., each nucleus icith its allotted quantity of 
protoplasm, is embedded in a matrix of intercellular sub- 
stance. 

Inasmuch as during the growth of cartilage the cells 
remain soft and protoplasmic, while the intercellular sub- 



INTERIOR TISSUES. 



321 



stance is converted into a solid semi-transparent hard mat- 
ter, it comes to pass that the soft nucleated cells appear 
to lie in cavities in the harder intercellular substance or 
matrix. 

In epithelium it is only the deepest-lying cells which 
undergo division, and so carry on the growth of the tissue. 
In cartilage, cell - division is much more general ; a cell 
lying in its cavity divides first into two, then into four, 
and so on, the intercellular substance meanwhile growing 
in between the young cells and thrusting them apart. It 
is by means of the repeated divisions of the cells in this 
way, and subsequent development of intercellular matrix 
in between the young cells, that cartilage grows, Conse- 



* if 




Fig. 118. 

A lection of cartilage, showing the matrix ia\ with the groups of colls (b) containing 

nuclei (c) and fat-globules (d). (Magnified about three hundred and fifty diameters.) 



quently, the cells are frequently seen arranged in groups 
with more or less matrix between, according to their age. 

The cells remain during life soft and protoplasmic, but 
often contain a number of large oil-globules. It is to the 
hard matrix which yield.-, on boiling, the substance chon- 
drine, thai the physical features of cartilage, its solidity 
and elasticity, are due. Cartilage contains no vessels, or 
only such as extend a little way into it from adjacent 

part-. 

346. Connective Tissue. — Connective tissue (also called 

21 



322 



ELEMENTARY PHYSIOLOGY. 



fibrous, or areolar, or sometimes cellular tissue), the most 
extensively diffused of all in the body, at first sight seems 
to differ wholly from the preceding tissues. Viewed under 
the microscope, it is seen to consist of bands or cords, or 
sheets of whitish substance, having a wavy, fibrous appear- 
ance, and capable of being split up mechanically into innu- 
merable fine filaments or fibrillar. The addition of acetic 
acid causes it to swell up and become transparent, entirely 







Fig. 114. 

Connective Ttsstte. 

A, unchanged : <r, connective tissue ; £>, fat-cells. B, acted upon by acetic acid, and 
showing (a} the swollen and transparent gelatine-yielding matter, and (b) the elastic 
fibres. (Magnified about three hundred diameters.) 

losing its fibrous aspect ; and, further, reveals the presence 
of two elements which acetic acid does not affect, viz., 
nuclei and certain sharply-defined fibres of different degrees 
of fineness, which are called elastic fibres. If the acid be 
now very carefully neutralized by a weak alkali, the con- 
nective tissue assumes its former partial opacity and fibril- 
lated aspect. The nuclei thus brought to light by acetic 






INTERIOR TISSUES, 



323 



acid arc worthy of attention, because careful examination 
shows that they belong to certain cells which exist in all 
connective tissue in greater or less Dumber, though never 
in abundance. These cells, generally called connective~tis- 
corpusdeS) consist of a nucleus and protoplasmic cell- 
substance, and in fact are not unlike cartilage-cells except 
that they are very often very irregular in form, and as a gen- 
eral rule very small. Indeed, we may very justly compare 
connective tissue with cartilage, much as they seem to dif- 
fer in general appearance. The connective-tissue corpuscles 




Vu,. 11.".. 

Connective-tissue eorpusr-k-s (a. nucleus, f>. cell-substances), of various shapes, those to 
the right hand branching, and the branches joining. 



correspond to the cartilage-cells; both are embedded in a 
matrix which, in the case of cartilage, remains structure- 
3, but becomes solid and dense, while it, in the case of 
inective tissue, is altered or metamorphosed, as it is 
I, into a Bubstance composed of excessively lino fila- 
ments, mingled with which are elastic fibres. 

The fine fibrillate 1 substance i> not very clastic, and 
when boiled swells up and yields gelatine* The elastic 



324 



ELEMENTARY PHYSIOLOGY. 



fibres do not yield gelatine, and, as their name indicates, 
are highly elastic. The proportion of elastic fibre to the 
gelatine-yielding constituents of connective tissue varies 
in different parts of the body. Sometimes it is so great 
that elasticity is the most marked character of the result- 
ing tissue. 

347. Ligaments and Tendons, — Ligaments and tendons 
are simply cords, or bands, while fascice are sheets of very 
dense connective tissue. In some parts of the body, the 
connective tissue is more or less mixed with, or passes 
into, cartilage, and such tissues are called jibro-cartilages 
{see Chapter VII.), or, in other words, the matrix of the 
cartilage becomes more or less fibrillated, thus indicating 
the analogies of the two tissues. 

The name cellular applied to this tissue is apt to lead 
to confusion. When first used it referred to the cavities 
left in the meshes of the net-work of fibres ; it has nothing 
whatever to do with cells technically so called. 

348. Fat-Cells. — Fat -cells are scattered through the 




A, having their natural aspect. B, collapsed, the fat being* exhausted. C, with 
fatty crystals. The nuclei are not seen in this case. (Magnified about three hundred 
and fifty diameters.) 

connective tissue, in which they sometimes accumulate in 
great quantities. They are spheroidal sacs, composed of a 
delicate membrane, on one side of which is a nucleus, and 
distended by fatty matter, from which the more solid fats 



INTERIOR TISSUES. 



325 



sometimes crystallize out after death. Ether will dissolve 
out the fat, and leave the sacs empty and collapsed (B, 
Fig. 116). 

They are, in fact, cells with a distinct cell- wall, the cell- 
contents or cell-substance of which have been wholly, or 
all but wholly, converted into fat. 

Considerable aggregations of fat-cells are constantly 
present in some parts of the body, as in the orbit, and 




Fig. 117. 
Capillaries of Fat. 

A. net-work round a proup of fat-cells : a. the artery ; h. the vein. B, the loops of 

capillaries round three individual fat-ceils. 

about the kidneys and heart ; but elsewhere their presence, 
in any quantity, depends very much on the state of nutri- 
tion. Indeed, they may be regarded simply as a reserve, 
formed from the nutriment which has been taken into the 
body in excess of its average consumption. 

349. Pigment-Cells. — Pigment-cells are either epidermic 
or epithelial cells, in which colored granules arc deposited, 
or they arc oonnective^tissue corpuscles of the deeper parts 
of the body, in which a like deposit occurs. Thus the color 
of the choroid arises partly from the presence of a layer 

Of epithelial Cells (see Fig. 93), placed close to the retina. 

containing pigment -granules, and partly from a large 



326 ELEMENTARY PHYSIOLOGY. 

number of irregularly- shaped, connective-tissue corpuscles 
crammed with pigment, which belong to the deeper con- 
nective-tissue layer of the choroid. The pigment-cells of 
the frog's web are essentially connective-tissue corpuscles. 

Section III. — Osseous Tissues. 

350. Structure of Bone. — Bone is essentially composed 
of an animal basis impregnated with salts of carbonate and 
phosphate of lime, through the substance of which are 
scattered minute cavities — the lacunce, which send out 
multitudinous ramifications, called canaliculL The cana- 
liculi of different lacunar unite together, and thus establish 
a communication between the different lacunae. If the 
earthy matter be extracted by dilute acids, a nucleus may 
be found in each lacuna ; and, if young, fresh bone be care- 
fully examined, a certain amount of cell-substance will be 
found filling up the lacuna round the nucleus ; and, not 
unfrequently, the intermediate substance appears minutely 
fibrillated. In fact bone, if we lay on one side the earthy 
matters, presents very close analogies in its fundamental 
structure with both cartilage and connective tissue. The 
corpuscles lodged in the lacunae correspond to the corpus- 
cles of connective tissue and to the cells of cartilage, while 
the matrix in which the earthy matter is deposited corre- 
sponds to the matrix of cartilage, and to the fibrillated 
material of connective tissue. (These three tissues, in- 
deed, are often classed together as " the connective-tissue 
group.") In a dry bone the lacunae are usually filled with 
air. When a thin section of such a bone is, as usual, cov- 
ered with water and a thin glass, and placed under the 
microscope, the air in the lacunae refracts the light which 
passes through them in such a manner as to prevent its 
reaching the eye, and they appear black. Hence the 
lacunae were, at one time, supposed to be solid bodies, 
containing the lime-salts of the bone, and were called 
bone-corpuscles (Fig. 118, C). 



36SOUS TISSUES 

All bones, except tlie smallest, are traversed by small 
canals, converted by side-branches into a net-work, and 
containing vessels supported by more or less connective 
tissue and fatty matter. . 5 re called Haversian canaU 
(Fig. 118. A, B). They always open, in the long-run, upon 
the surface of the bone, and there the vess - which they 
contain become connected with those of a she* I of tough 
connective tissue, which invests the bone, and is called 
tm. 

In many long bones, such as the thigh-bone, the centre 
of the bone is hollowed out into a considerable cavity, 
containing great quantities of fat, supported by a delicate 
connective tissue, rich in blood-vessels, and called the mar- 
edulla. The inner ends of the Haversian canals 
communicate with this cavity, and their vessels are con- 
tinuous with those of the marrow. 

When a section of a bone containing Haversian canals 
is made, it is found that the lacuna? are di- 
centric zones around each Haversian canal, so that the 
substance of the bone appears laminated : and. where a 
medullary cavity exists, more or fewer of these concentric 
lamellae of osseous substance surround it. 

351. How Bones grow. — This structure arises from the 
mode of growth of bones. In the place of every bone 
there exists, at first, either cartilage, or connective tissue 
hardly altered from its primitive condition of indifferent 
tissue. When ossification commences, the vessels from 

adjacent parts extend into the ossifying and the 

calcareous salts arc thrown down around them. These 
cal -alts invade all the ossifying tissue, the 

immediate neighborhood of it- nuclei, around each of which 

. the la ■'//"/. i- left The lacunae and canaliculi 
thus, substantially, gaps left in th around 

b nucleus, whence it i- that nuclei are found in the la- 
cuna* of fully-formed boo 

- the sakeof «imp: <»ndary 

in the ossification of rartilage. 



328 



ELEMENTARY PHYSIOLOGY. 



Bone, once formed, does not remain during life, but is 
constantly disappearing and being replaced in all its parts. 



A. 









u 



:!w^'y, ^#h 




B. 




T «* 111! 




Fig. 118. 

A. — A transverse section of bone in the neighborhood of two Haversian canals, or, a ; 
6, lacunas. (Magnified about two hundred and fifty diameters.) 

B— A longitudinal section of bone with Haversian canals, a, a, and lacuna?, b. 
(Magnified about one hundred diameters.) 

C— Lacunae, c, and canaliculi, d. (Magnified about six hundred diameters.) 



OSSEOUS TlssrES. 329 

Nevertheless, the growth of a bone, as a general rule, takes 
plaee only by addition to its free ends and surfaces. Thus 
the bones of the skull grow in thickness, on their surfaces, 
ami in breadth at their edges, where they unite by Stitures f 

and. when the sutures are once closed, they ce ise to in- 
crease in breadth. 

The bones of the limbs, which are preceded by complete 
small cartilaginous models, grow in two ways. The car- 
tilage of which they consist grows and enlarges at its ex- 
tremities until the bones have attained their full size, and 
remains to the end of life as articular cartilage. But, in 
the middle, or shaft, of the bone, the cartilage does not 
grow with the increase in the dimensions of the bone, but 
the small primary bone which results from the ossification 
of the cartilaginous model becomes coated by successive 
layers of bone, produced by the ossification of thai part of 
the periosteum which lies nearest to it, and which really 
consists of indifferent tissue — that is, of nuclei embedded 
in a matrix. The shaft of the bone thus formed is gradu- 
ally hollowed out in its interior to form the medullary 
cavity, so that, at last, the primitive cartilage totally dis- 
appears. 

When ossification sets in, the salts of lime are not dif- 
fused uniformly through the whole mass of the preexisting 
cartilage, or connective tissue,. but begin to be deposited 
at particular points called centres of ossification^ and spread 
from them through the bone. Thus, a long bone has usu- 
ally, at fewest, three centres of ossification — one for the 
middle, Or shaft, and one for each end; and it is only in 
adult life that the three bony mas. -s thus formed unite 

into one bone. 

352. Structure of the Teeth.— Teeth partake more of 

the nature of 'hours than of any other organ, and are. in 
.partially composed of true bony matt r, here called 
-///; but their chief canal ituent- are two other tissues, 

called dentim and < n<i,,,< /. 



330 



ELEMENTARY PHYSIOLOGY. 



Each tooth presents a crown, which is exposed to wear, 
and one or more fangs, which are buried in a socket fur- 
nished by the jaw-bone and the dense mucous membrane 
of the mouth, which constitutes the gum. The line of 
junction between the crown and the fang is the neck of 
the tooth. In the interior of the tooth is a cavity, which 
communicates with the exterior by canals, which traverse 
the fangs and open at their points. This cavity is the pulp 
cavity. It is occupied by a highly-vascular and nervous 
tissue, the dental pulp, which is continuous below, through 
the openings of the fangs, with the mucous membrane of 
the gum. 

B 
JQ d 

J* 




Fig. 119. 

A, vertical, B, horizontal section of a tooth : a. enamel of the crown; 5, pulp cavity; <s, 
cement of the fangs , d, dentine. (Magnified about three diameters.) 

The chief constituent of a tooth is dentine — a dense 
calcined substance containing less animal matter than bone, 
and further differing from it in possessing no lacunae, or 
proper canaliculi. Instead of these it presents innumera- 
ble, minute, parallel, wavy, tubules, which give off lateral 
branches. The wider ends of these tubules open into the 
pulp cavity, while the narrower ultimate terminations ramify 
at the surface of the dentine, and may even extend into 
the enamel or cement (Fig. 120, C). 






OSSEOUS TISSUES 



331 



The entMfnd consists of wry small six sided fibres, set 
closely, side by side. Dearly at right angles to the surface 
of the dentine, and covering the crown of the tooth as far 

as the neck, towards which the enamel thins off and joins 
the cement (Fig. 120, A, B). 

Enamel is the hardest tissue of the body, atid contains 
not more than two per cent, of animal matter. 






Yu. 

A .- ' -n. 

I'.. — Enamel fll illy. 

a ;?h th<» cement (4 : 6, & 

irpegular cavities in arnica thetubnlei ratine end; rf.flne fcnbnJea continued 

una- and an. LDOUt lour bandied 



332 ELEMENTARY PHYSIOLOGY. 

The cement coats the fangs, and has the structure of 
true bone ; but, as it exists only in a thin layer, it is devoid 
of Haversian canals (Fig. 120, C). 

353. How Teeth are developed. — The development of 
the teeth commences long before birth. A groove appears 
in the gum of each side of each jaw ; and, at the bottom 
of this groove of the gum, five vascular and nervous pa- 
pillae, arise, making twenty in all. The walls of the groove 
grow together, between and over each of the papillae, and 
thus these become inclosed in what are called the dental 
sacs. 

Each papilla gradually assumes the form of the future 
tooth. Next, a deposit of calcific matter takes place at the 
summit of the papillae, and extends thence downwards tow- 
ards its base. In the crown the deposit takes on the form 
of enamel and dentine ; in the root, of dentine and cement. 
As it increases it encroaches upon the substance of the pa- 
pilla, which remains as the tooth pulp. The fully-formed 
teeth press upon the upper walls of the sacs in which they 
are inclosed, and, causing a more or less complete absorp- 
tion of these walls, force their way through. The teeth 
are then, as it is called, cut. 

The cutting of this first set of teeth, called deciduous, 
or milk-teeth, commences at about six months, and ends 
with the second year. They are altogether twenty in num- 
ber, eight being cutting teeth, or incisors ; four, eye-teeth, 
or canines ; and eight, grinders, or molars. 

Each dental sac of the milk-teeth, as it is formed, gives 
off a little prolongation, which becomes lodged in the jaw, 
enlarges, and develops a papilla from which a new tooth 
is formed. As the latter increases in size, it presses upon 
the root of the milk-tooth which preceded it, and thereby 
causes the absorption of the root and the final falling out, 
or shedding of the milk-tooth, whose place it takes. Thus, 
every milk-tooth is replaced by a tooth of what is termed 
the permanent dentition. The permanent incisors and ca- 









MUSCULAR AND NERVOUS TISSUES. 333 

nines are larger than the milk-teeth of the same name, but 
otherwise differ little from them. The permanent molars, 
which replace the milk-molars, are small, and their crowns 
have only two points, whence they are called bicuspid. 
They never have more than two fangs. 

354. The Permanent Molars. — We have thus accounted 
for twenty of the teeth of the adult. But there are thirty- 
two teeth in the complete adult dentition, twelve grinders 
being added to the twenty teeth which correspond with, 
and replace, those of the milk-set. AVhen the fifth, or 
hindermost, dental sac of the milk-teeth is formed, the part 
of the groove which lies behind it also becomes covered 
over, extends into the back part of the jaw, and becomes 
divided into three dental sacs. In these, papilhe are 
formed and give rise to the great permanent back grind- 
ers, or molars, which have four, or five, points upon their 
square crowns, and, in the upper jaw, commonly possess 
three fangs. 

The first of these teeth, the anterior molar of each side, 
is the earliest cut of all the permanent set, and appears at 
six years of age. The last, or hindermost, molar is the last 
of all to be cut, usually not appearing till twenty- one or 
twenty-two years of age. Hence it goes by the name of 
the " wisdom-tooth." 

Section IV. — Muscular mxl Xervous Tissues. 

355. Muscle, Striated and Smooth. — Muscle is of two 
kinds, striated, or striped, and smooth, plain, ot imxtriated. 
Striated muscle, of which all the ordinary muscles of the 

trunk and limbs consist, IS composed of a number of long 

parallel cylindrical fibres, culled elementary or ultimate 
muscular fibres, which are bound together by connective 
tissue into small bundles. These small bundles again are 
united into larger bundles, and these into one aggregate, 
by connective tissue, which supports the vessels and nerves 
of the muscle, and usually forms at one or both ends of the 



334 



ELEMENTARY PHYSIOLOGY. 



muscle a tendon (see 218), and sometimes gives rise to a 
dense sheath or fascia on its exterior. 

Into the ultimate muscular fibre neither vessels, nor con- 
nective tissue, enter. Each fibre is, however, enveloped in 
a sheath formed by a tough, elastic, transparent structure- 
less membrane, the sarcolemma (Fig. 121, D, b). 

The sarcolemma is not contractile, but its elasticity al- 



-Ji 



<^a ^r 




(xocoaxco 





Fig. 121. 

A. a muscular fibre, devoid of sarcolemma, and breaking- up at one end into its fibril - 
l-z ; B, separate fibrillse; 0, a muscular fibre breaking- up into disks; D, a muscular 
fibre, the contractile substance of which (a) is torn, while the sarcolemma (&) has not 
given way. (Magnified about three hundred and fifty diameters.) 



lows it to adjust itself, pretty accurately, to the changes of 
form of the contractile substance which it contains. 

This contractile substance, when uninjured, presents a 
very strongly-marked transverse striation, its substance ap- 
pearing to be composed of extremely minute disks of a 
partially opaque substance, embedded at regular intervals in 






MUSCULAR AND NERVOUS TISSUES. 



335 



a more transparent matter. A more taint striation, separat- 
ing these disks into longitudinal series, is also observable. 
When the sarcolemma is torn, the contractile substance 
of dead muscle may, under some circumstances, be di- 
vided into disks (Fig. 121, C), but it may be more readily 
broken up into minute JibrillcB (Fig, 121, A, B), each of 
which, viewed by transmitted light, presents dark and lio-ht 
parts, which alternate at intervals corresponding with the 




In.. 122. 



Capillabibs of Striated Muscle. 



a — Seen longitudinally. The width of Che meshes corresponds to that of an ulti- 
mate fibre. ". BmaU artery : h. small vein. 

B.— Transverse section muscle. </. the cut ends of the ultimate fibres; 

tpQtariefl filled with injection material: <-. parts where the capillariea are absent or 
led. 

distances of the transverse striae in the entire fibre. Nuclei 
are observed here and there in the contractile substance 
within the sarcolemma. 

In tin- heart, tin* muscular fibres are striated, and have 
the - sential structure as thai jusl described, but they 

no sarcolemma. 

Smooth mu8cli consists of elongated band-like fibres, 
devoid of striation, each of which bears a rod-like nucleus. 



336 



ELEMENTARY PHYSIOLOGY. 



These fibres do not break up into fibrillar, and have no sar- 
colemma (Fig. 123). 




Fig. 123. 

Smooth or non-striated muscular fibres from the middle coat of a small artery; the 
middle one, having been treated with acetic acid, shows more distinctly the nucleus, a. 
(Magnified about three hundred and fifty diameters.) 

356. Nervous Tissue. — Nervous tissue contains two ele- 
ments, nerve-fibres and ganglionic corpuscles. Ordinary 
nerve-fibres, such as constitute the essential constituents 
of all the cerebro-spinal nerves except the olfactory, are 
during life, or when perfectly fresh, subcylindrical filaments 
of a clear, somewhat oily, look. But, shortly after death, 
a sort of coagulation sets up within the fibre, and it is then 
found to be composed of a very delicate, structureless, outer 
membrane (which is not to be confounded with the neuri- 
lemma), forming a tube, through the centre of which runs 
the axis-cylinder, which is probably composed of an aggre- 
gation of very fine filaments. Between the axis-cylinder 
and the tube is a fluid, rich in fatty matters, from which a 
solid strongly-refracting substance has been thrown down 
and lines the tube. 

Such is the structure of all the larger nerve-fibres which 
lie, side by side, in the trunks of the nerves, bound together 



MUSCULAR AND NERVOUS TISSUES. 



337 



by delicate connective tissue, and inclosed in a sheath of 
the same substance, called the neurilemma. In the trunks 
of the nerves, the fibres remain perfectly distinct from one 
another, and rarely, if ever, divide. But, when the nerves 
enter the central organs, and when they approach their 
peripheral terminations, the nerve-fibres frequently divide 
into branches. In any case they become gradually finer 
and finer, until, at length, axis-cylinder, sheath, and con- 
tents, are no longer separable, and the nerve-fibre is reduced 




,:-V 






r», 124. 

Papilla of the Skin of the Fingee. 

a. a lanre papilla containing a tactile corpuscle (s) with its nerve (<7) ; b. other pa- 

Eilla\ without corpuscles, but containing loops of \ a Lout three 

undred diameter.-. | 

to a delicate filament, the ultimate termination of which, 
in the sensory organs and in the muscles, is not yet thor- 
OUgfaly made out. 

357. Tactile Corpuscles.— In Chapter VIII. (239), men- 
tion i- made of peculiar bodies called tactik corpuscles, 
which ait* oval masses of specially modified connective 

ie in relation with the ends of the nerves in the pa- 
pillae of the skin. In Fig, I'M four Blich papillae, which 
have been rendered transparent and stripped of their epi- 



338 



ELEMENTARY PHYSIOLOGY. 



dermis, are seen, and the largest contains a tactile cor- 
puscle (e). The mode in which nerves, not connected with 
tactile corpuscles, end in the skin, is not definitely known. 

In muscles, the nerve-fibre seems to pierce the sarco- 
lemma, and to end inside the ultimate muscular fibre in a 
peculiar knob or plate. 

In the brain and spinal cord, on the other hand, it is 
certain that, in many cases, the ends of the nerve fibres are 
continued into the processes of the ganglionic corpuscles. 

358. The Olfactory Nerves— The olfactory nerves are 
composed of pale, flat fibres without any distinction into 
axis-cylinder and contents, but with nuclei set at intervals 
along their length. 



A 

llil 



E 










Fig. 125. Fig. 126. Fig. 127. Fig. 128. 

Fig. 125. — A nerve-fibre in its fresh and unaltered condition. 

Fig. 126.— A nerve-fibre in which the greater part of the sheath and coagulated con- 
tents (a l>) have been stripped off from the axis-cylinder (c c). 

Mg. 127. — A nerve-fibre. the«»pper part of which retains its sheath and coagulated 
contents, while the axis-cylinder (a a) projects. 

Fig. 128. — A ganglionic corpuscle — a, its nucleus and nucleolus. (Magnified about 
350 diameters.) 






ANATOMICAL AND PHYSIOLOGICAL CONSTANTS. 339 

Similar fibres are found in the sympathetic nerves, 
mingled with fibres of the same structure as those of the 
spinal nerves. 

359. Ganglionic Corpuscles. — Ganglionic corpuscles are 
chiefly found in tin 1 cerebro-spinal axis ; in the ganglia of 
the posterior nerve-roots, and in those of the sympathetic; 
but they occur also elsewhere, notably in some of the sen- 
sory organs {see Chapter IX.). 

They are spheroidal bodies, consisting of a soft semi- 
solid cell-substance, in the midst of which is a large clear 
and transparent area usually termed the nucleus. Within 
the nucleus again is generally a smaller body commonly 
termed the nucleolus (Fig. 128, a). Each ganglionic cor- 
puscle sends off one, two, or more prolongations^ which 
may divide and subdivide ; and which, in some cases, unite 
with the prolongations of other ganglionic corpuscles, while, 
in others, they are continued into nerve-fibres. 



CHAPTER XIII. 

ANATOMICAL AM) PHYSIOLOGICAL CONSTANTS. 

360. General Statistics. — The weight of the body of a 
full-grown man may be taken at 154 pounds. 
Such a body would be made up of — 

Pounds. 
Musclea and their appurtenances . . . .68 

Skeleton 24 

Skin 10} 

Pal 

in 3 

i ...... . 

Abdominal viaa • .i . . . . . .11 

1J7 1 
of blood, the quantity which win readily drain away 
• [54 pounds L considerable quantity of blood 



340 ELEMENTARY PHYSIOLOGY. 

Or of— 

Pounds. 

Water 88 

Solid matters 66 

The solids would consist of the elements oxygen, hy- 
drogen, carbon, nitrogen, phosphorus, sulphur, silicon, 
chlorine, fluorine, potassium, sodium, calcium (lithium), 
magnesium, iron (manganese, copper, lead), and may be 
arranged under the heads of — 

Proteids. Amyloids. Fats. Minerals. 

Such a body would lose in 24 hours — of water, about 
40,000 grains, or 6 pounds ; of other matters about 14,500 
grains, or over two pounds ; among which of carbon 4,000 
grains ; of nitrogen 300 grains ; of mineral matters 400 
grains ; and would part, per diem, with as much heat as 
would raise 8,700 pounds of water 0° to 1° Fahr., which is 
equivalent to 3,000 foot-tons. 1 Such a body ought to do as 
much work as is equal to 450 foot-tons. 

The losses would occur through various organs, thus— by 







Other 








Water. 


Matter. 


N. 


C. 




Grains. 


Grains. 


Grains. 


Grains. 


Lungs . 


5,000 


12,000 




3,300 


Kidneys . 


23,000 


1,000 


250 


140 


Skin . 


10,000 


700 


10 


100 


Faeces 


2,000 


800 


40 


460 



Total . . 40,000 14,500 300 4,000 

The gains and losses of the body would be as follows : 

Grains. 

Creditor— Solid dry food 8,000 

Oxygen 10,000 

Water 36,500 



Total 54,500 

will, however, always remain in the capillaries and small blood-vessels, and must be 
reckoned with the various tissues. The total quantity of blood in the body is now 
calculated at about l-13th of the body weight, i. e.. about 12 pounds. 

1 A foot-ton is the equivalent of the work required to lift one ton one foot high. 



ANATOMICAL AND PHYSIOLOGICAL CONSTANTS. 841 

Grains. 
Debtor— Water 40,000 

Other matters ..... 14,500 

Total 54,500 

361. Digestion. — Such a body would require for daily 
food, carbon 4,000 grains, nitrogen 300 grains ; which, 
with the other necessary elements, would be most con- 
veniently disposed in — 

Grains. 

Proteida 2,000 

Amyloids 4,400 

Fats 1,200 

Minerals 400 

Water 36,500 

Total 44,600 

which, in turn, might be obtained, for instance, by means 

Grains. 

Lean beefsteaks . ." 5,000 

Bread 6,000 

Milk 7,000 

Potatoes 3,000 

Butter, dripping, etc. 600 

Water 22,900 

Total 44,500 

The feces passed, per diem, would amount to about 
1 grains, containing solid matter 800 grains. 

362. Circulation. — In such a body the heart would beat 
75 times a minute, and probably drive out, at each stroke 
from each ventricle, from 5 to 6 cubic inches, or about 

grains of blood. 
The blood would probably move in the great arteries 
at a rate of about 1"2 inches in a second, in the capillaries 

at 1 to 1' inch in a minute; and the time taken up in 
performing the entire circuit would probably be about 30 

uds. 



342 ELEMENTARY PHYSIOLOGY. 

The left ventricle would probably exert a pressure on 
the aorta equal to the pressure on the square inch of a 
column of blood about 9 feet in height ; or of a column of 
mercury about 9^ inches in height ; and would do in 24 
hours an amount of work equivalent to about 90 foot-tons ; 
the work of the whole heart being about 120 foot-tons. 

363, Respiration, — Such a body would breathe 15 times 
a minute. 

The lungs would contain of residual air about 100 cubic 
inches, of supplemental or reserve air about 100 cubic 
inches, of tidal air 20 to 30 cubic inches, and of comple- 
mental air 100 cubic inches. 

The vital capacity of the chest — that is, the greatest 
quantity of air which could be inspired or expired — would 
be about 230 cubic inches. 

There would pass through the lungs, per diem, about 
350 cubic feet of air. 

In passing through the lungs, the air would lose from 
4 to 6 per cent, of its volume of oxygen, and gain 4 to 5 
per cent, of carbonic acid. 

During 24 hours there would be consumed about 10,000 
grains oxygen ; and produced about 12.000 grains carbonic 
acid, corresponding to 3,300 grains carbon. During the 
same time about 5,000 grains or 9 ounces of water would 
be exhaled by the lungs. 

In 24 hours such a body would vitiate 1,750 cubic feet 
of pure air to the extent of 1 per cent., or 17,500 cubic feet 
of pure air to the extent of 1 per 1,000. Taking the amount 
of carbonic acid in the atmosphere at 3 parts, and in ex- 
pired air at 470 parts in 10,000, such a body would require 
a supply per diem of more than 23,000 cubic feet of or- 
dinary air, in order that the surrounding atmosphere might 
not contain more than 1 per 1,000 of carbonic acid (when 
air is vitiated from animal sources with carbonic acid to 
more than 1 per 1,000, the concomitant impurities become 
appreciable to the nose). A man of the weight mentioned 



ANATOMICAL AND PHYSIOLOGICAL CONSTANTS. 343 

(11 stone) ought, therefore, to have at least 800 cubic feet 
of well-ventilated space. 

364. Cutaneous Excretion. — Such a body would throw 
off by the skin — of water about 18 ounces, or 10,000 
grains ; of solid matters about 300 grains ; of carbonic acid 
about 400 grains, in 24 hours. 

365. Renal Excretion. — Such a body would pass by the 
kidneys — of water about 50 ounces; of urea about 500 
grains ; of other solid matters about 500 grains, in 24 
hours. 

366. Nervous Action. — In the frog a nervous impulse 
travels at the rate of about 80 feet in a second. 

In a man a nervous (sensory) impulse has been variously 
calculated to travel 100, 200, or 300 feet in a second. 

387. Histology. — Red corpuscles of the blood are about 
y^nfth of an inch in breadth ; white corpuscles 8 / 06 t h. 

Striated muscular fibres are about j-J-Q-tk of an inch in 
breadth ; plain xoVo 1 ^ 1 - 

Xerve-fibres vary between 15 1 00 th and -j-gL-tk 0I " an 
inch in breadth. 

Connective tissue fibrils are about 4 fo o^ ° °f an mcu ^ n 
breadth. 

Epithelium scales (of the skin) are about -g^th of an 
inch in breadth. 

Capillar blood-vessels are from 3 fo ^t h to g fa t h of an 
inch in breadth. 

Cilia (from the windpipe) are about -joVo^ 1 °f an nicn 
in length. 

The cones in the "yellow spot" of the retina are about 

17th of an inch in breadth. 



PART II. 
ELEMENTARY HYGIENEo 



CHAPTER XIV. 

SCOPE AND AIMS OF HYGIENE. 

368. Applied Physiology. — Thus far the student has 
been occupied in getting an understanding of the truths 
of physiological science, or of the actions of the living sys- 
tem in normal conditions. This knowledge has two great 
practical applications : the first to Hygiene, or the art of 
preserving health ; and the second to Medicine, or the art 
of restoring it. When the vital machine has once become 
seriously deranged, profound knowledge and great skill 
and experience may be required to set it right again, and 
this is the work of the physician, who has to devote his 
lite to professional study. But, happily, it requires less 
knowledge to keep what we already have than to recover 
it when lost. How to take care of the health, or to avoid 
many causes of disease, may be learned by all. That gen- 
eral acquaintance with the mechanism and working of the 
living system, which all persons, even moderately educated, 
should possess, is not only valuable to guard it against in- 
jury, but also to improve its various powers and capabili- 






SCOPE AXD AIMS OF HYGIENE 345 

ties. If life and its opportunities be valuable, what knowl- 
edge can compare in importance with that which teaches 
how it is to be prolonged, and its various capacities aug- 
mented ? 

369. False Conceptions of Disease. — In early ages it 
was the custom to explain all effects in Nature by suppos- 
ing personalities like our own which produce them. The 
air, the earth, the forest, the streams, the sea, wore peo- 
pled with imaginary beings, who were believed to be the 
agents by which all the operations of Nature were carried 
on. The regular actions of the living system were thought 
to be due to spirits which inhabited it, and its disorders 
to the agency of evil spirits. Though these superstitions 
long since passed away, the ideas which replaced them 
involved errors of a kindred nature. Diseases were no 
longer considered as personal agencies to be driven out 
bv exorcism, but there still lingered the idea that they 
were things, independent existences or entities, which 
were in some mysterious way thrust into the system, and 
" expelled n from it by the action of medicines. Vague 
notions of this kind still widely prevail, and great num- 
bers regard diseases as things that come arbitrarily, or 
are u sent " by Divine Providence as judgments or punish- 
ments for sins. 

Views of this kind are unfavorable to hygienic efforts. 
v > e c&n easily understand that minds fully possessed by 
them irfl] tend to a passive acquiescence in what is felt to 
be unavoidable, and the propitiation of Divine favor, by 
ting", humiliations, and prayers, will take the place of 
intelligent^ vigilant, and systematic measures for the pre- 
vention of disease. In past times, indeed, such notions 
have operated as powerful hinderances to hygienic precau- 
tions. When quarantine regulations were firsl instituted 
t" prrvt'iit the spread of contagion by ships from port to 

port, and when vaccination was proposed a- a preventive 

of small-pox. religious ideas were aroused into antagonism. 



346 ELEMENTARY HYGIENE. 






and these beneficent measures were denounced as impiously 
contravening the Divine designs which employed plagues 
as scourges to punish the transgressions of mankind. In 
this way false theories of the nature and causes of disease 
acted as an obstruction to hygienic improvement. 

370. The True Idea of Health and Disease. — Modern 
physiology has brought us to a better understanding of the 
subject. As we have seen, throughout the foregoing pages, 
physiology is the science of vital power. Power is the ac- 
companiment of materiai change, and the manifestation of 
all animal functions is dependent upon vital transforma- 
tions. Not only is the living body in constant visible move- 
ment, but in all its minutest parts and tissues there is an 
incessant metamorphosis — a rapid escape and renewal of 
the constituent atoms, and it is in this that life essentially 
consists. That active and unimpeded metamorphosis and 
prompt elimination of waste products which give rise to 
the highest and most vigorous life constitute Health ; 
while the obstruction, depression, or perversion of these 
vital changes constitutes Disease. We thus escape from 
the mischievous error that maladies are foreign intrusions 
—substantive existences which get mysterious lodgment 
in the living organism, and find that they are simply dis- 
turbed physiological actions. A disease may consist in the 
loss of power to remove or excrete normal but injurious 
products; or perverted transformations may give rise to 
wrong products, and these may create still further dis- 
turbance, but in all cases the essence of disease is to be 
regarded as abnormal activity. 

Gout, for example, is a malady in which bad habits per- 
vert the nutritive changes and originate morbid products ; 
its chief peculiarity being the deposition of urate of soda in 
and about the joints. In health there is scarcely a trace 
of this salt to be found in the blood, and even this small 
proportion is being constantly thrown off. Certain con- 
ditions of living, however, such as the habitual use of w T ines 



SCOPE AND AIMS OF HYGIENE. 34 7 

or malt liquors, and high feeding upon animal substances, 
attended with but little exercise, are known greatly to in- 
crease its quantity and seriously to interfere with its excre- 
tion. It is then deposited as a foreign, or morbid, ingre- 
dient in the joints. Careful avoidance of the causes which 
give rise to this condition of the blood secures complete 
freedom from attack, even in those who may have inherited 
a strong predisposition to the disease. 

371 Control over the Causes of Disease. — We have seen 
how directly the great functions of the system depend upon 
various conditions, such as diet, air, water, clothing, and ex- 
ercise, by which the healthy changes of life are carried for- 
ward. These agencies, in their right action, are causes of 
health ; but, when altered in their influence, they become 
causes of disease. The gases, liquids, and solids, which 
maintain the transformations of life, if deficient in quan- 
tity or deteriorated in quality, speedily produce bodily de- 
rangement ; while just in. proportion to the importance of 
these normal actions is the evil which results from their 
perversion. By the power which intelligence confers over 
these conditions, man may in great measure control the 
causes of disturbed health. Diseases may baffle the physi- 
cian's penetration and defy his remedial skill; but, what 
is of far more importance, hygienic knowledge enables us 
to avoid them. The efficiency of prevention is proverbial, 
and we have examples of the value of sanitary knowledge 
and precautions on the most impressive scale. 

372. Examples of the Application of Hygienic Principles. 
— Cholera may be taken as an illustration. In former 
times, when sanitary questions were but little understood, 
the approach of this terrible disease was viewed with a 
horrible dread; and, paralyzed with fear, the people did 
nothing to stay it- advance. When it appeared, medicines 
were the only remaining resource, and, in spite of their 

. the pestilence swept away multitudes of the popula- 
tion of the principal town-. But the connection between 



348 ELEMENTARY HYGIENE. 

the disease and certain conditions, as filth, bad air, over- 
crowding, and irregularities of living, so common in cities, 
began at length to be perceived, and steps taken to remove 
the causes. The adequacy of these measures has been fully 
vindicated, and, with the knowledge that its conditions 
are controllable, the predisposing alarms have ceased, the 
ravages of the epidemic have been greatly circumscribed, 
and there is the amplest experience to show that thorough, 
yet simple, measures of purification are sufficient for its 
complete prevention. 

Scurvy is another case in point. This disease, which, 
until recently, has been the scourge of the sailor and sol- 
dier, and for centuries was regarded as wholly beyond the 
power of remedies, also turns out to be fully preventable. 
" There is no more interesting fact in the history of medi- 
cine than that this condition, which has been looked upon 
at various times as plague, as a mysterious infliction of Di- 
vine justice, against which man could only strive in vain, 
or as a disease inseparable from long voyages, should have 
been proved by evidence of a most satisfactory character 
to arise from causes in the power of man to prevent, and 
to be curable by means which every habitable country af- 
fords." Instead of inquiring into the conditions of its 
origin, and seeking means of prevention, the medical pro- 
fession, for hundreds of years, was engaged in ransacking 
Nature, with the hope of finding something that might 
prove an effectual remedy. The search was fruitless until 
attention was turned to the cause of the disorder, which 
proved to be a lack of vegetable food, and the simple pre- 
caution of furnishing this has been the signal for the almost 
total disappearance of the disease. Many other illustra- 
tions might be given of the efficiency of hygienic resources 
to arrest and prevent the spread of dangerous maladies, 
but they are needless. 

373. Remedial Influence of Hygienic Agencies. — Another 
important consideration deserves to be stated in this place : 



SCOPE AXD AIMS OF HYGIENE. 349 

it is that hygienic measures have a most important reme- 
dial value. If the conditions of health, when modified or 
perverted, become causes of disease 1 , to whatever extent 
restorative medicines mav be desirable, it is certain that 
the first dictate of wisdom is to rectify these wrongly-acting 
conditions. Medical treatment, thus, has its hygienic re- 
sources, which, with the enlargement of rational experience, 
are coming into greater and greater prominence. All, who 
have watched the progress of the healing art in recent 
times, will note that among the most enlightened prac- 
titioners there has been a steadily diminishing confidence 
in medication, and an increasing reliance upon the sani- 
tary influence of Nature. It is notorious that in propor- 
tion to people's ignorance of their own constitutions and 
the true causes of disease, is their credulous confidence 
in pills, potions, and quackish absurdities, and, while this 
ignorance continues, there will of course be plenty of doc- 
tors who will pander to it. And, not the least of the bene- 
fits likely to follow the better diffusion of physiological and 
sanitary information will be, the protection of the com- 
munity from the numberless impostures of charlatanism, 
and a better discrimination of the qualifications of com- 
petent physicians. 

374. The Sources of Ill-Health. — The more important ma- 
terial agencies and conditions, closely related to the processes 
of life, arc air, water, food, clothing, exercise, climate, soil, 
and occupation. Some of these, such as air and food, are 
indispensable; others, like clothing and exercise, are re- 
quired to make existence tolerable, and all, when rightly 
adjusted, are favorable to health. But all are liable to 
changes of character thai make them dangerous to bodily 
well-being; and, the extent of the danger in the case of 

:i, when thus depraved, is fairly measured by the im- 
portance of the part it plays in healthy physiological ac- 
tion. Life cannol •_:<» on, for example, without air and 
food, and we accordingly find that both air and food, in 



350 ELEMENTARY HYGIENE. 

their vitiated states, are among the most common sources 
of disease. Clothing is not only a requisixe of civiliza- 
tion, but has come to have an important share in the regu- 
lation of certain physiological operations ; and, when not 
wisely adapted, it too acts as a disturber of the bodily 
peace. To inquire into the manner in which these various 
agencies suffer deterioration, and thus become converted 
into sources of disease, and to point out the methods to be 
pursued, in order to avoid their ill-effects, are the objects 
of the following chapters. 



CHAPTER XV. 

AIR AND HEALTH. 

Section I. — Composition and Office of the Air. 

375. Its Chief Constituents. — The chief constituents of 
the atmosphere are a pair of elements, oxygen and nitro- 
gen, and a pair of compounds, carbonic acid and watery 
vapor. The student will remember that, in treating of 
respiration (Chapter IV.), it was stated that oxygen forms 
twenty-one per cent, and nitrogen seventy -nine per cent., 
very nearly, of the bulk of the air. Oxygen is the life- 
sustaining element, and requires to be kept up to this 
standard for healthy respiration. Nitrogen is the nega- 
tive or diluting element of the air. The proportion of 
these constituents is tolerably constant, wherever the air 
is free from contaminating influences ; but the quantity of 
oxygen is always notably diminished in the air of towns. 
The amount of carbonic acid ranges from three to six parts 
in ten thousand. Its proportion is greater in the air of the 
highest mountains than in the air of plains, and in the air 
of towns than in country air. Saussure has also shown 
that air contains more carbonic acid at night than in the day- 



COMPOSITION AXD OFFICE OF THE AIR. 351 

time, more in summer than in winter, and more in dry than 
in rainy weather. The quantity of aqueous vapor is highly 
variable, and is mainly determined by temperature. When, 
at a given temperature, the air has all it can hold, it is said 
to be satiurati d. From fifty to seventy-five per cent, of the 
amount required for complete saturation is usually present, 
though the quantity frequently ranges both above and be- 
low these limits, and then the air becomes unpleasantly 
moist, or dry. as the ease may be. 

376. Its Minor Constituents. — Along with the above, 
natural air contains minute quantities of ammonia, mostly 
in combination with carbonic acid, sulphur, or chlorine. 
The proportion rarely exceeds one part in a million of air ; 
ozone (regarded as an allotropic farm of oxygen) is also 
reckoned a normal constituent. Spectrum analysis has 
shown that the salts of sodium are everywhere present in 
small amount, and traces of organic matter, either living 
or dead, are also generally found. Other substances, in 
minute quantities, are often present in the air of particular 
localities, but the foregoing constituents, in the proportions 
named, form the external atmosphere, or what is com- 
monly known as pure air. 

377. Office of Air in Respiration. — Air performs a double 
work in the respiratory process. We have learned that one 
of the essential conditions of life is waste of tissue, and this 
requires the presence of oxygen in every part of the or- 

:ism. The oxygen thus employed is furnished by the 

air, through the medium of the lungs and blood. But, as 

the work of oxidation goes on within the system, it is 

try that the resulting waste be speedily removed. 

And here, again, the air comes into play, receiving in the 

lui)L r< . in the place of the Oxygen yielded to the blood, 

ertain proportion of effete matter in the shape of car- 
bonic acid and watery vapor, which if carries forth into 
the external atmosphere, 

378. Its Action on Noxious Products.— Air performs a 



352 ELEMENTARY HYGIENE. 

scarcely less important service for the health of man, in 
the external world. Gaseous and vaporous emanations of 
all degrees of virulence are constantly pouring into it from 
numberless sources, and, if these were suffered to accumu- 
late, the earth w^ould soon become unfit for habitation. 
But, in the air itself, we have a purifying agency that is 
continually at work on the grandest scale. By means of 
winds and currents these dangerous contaminations are 
effectually dispersed, and thus brought in contact with 
oxygen are rapidly destroyed or rendered innocuous, by 
oxidation. It not only acts as a purifier of the living 
body, but, when left to itself, air is a cleanser of foul places 
everywhere. It is only when man, heedless of Nature's 
methods, hinders her processes of purification by artificial 
barriers, that this otherwise beneficent element becomes a 
source of danger and disease. 

Section II. — Impurities of the Air. 

379. Sources of its Impurities.— Air is rendered impure 
or uufit for respiratory purposes both by disturbance in the 
proportion of its normal constituents, and by many sub- 
stances in the shape of gases, vapors, and solid particles, 
which are thrown into it from a variety of sources. Those 
arising from the habitations and w r orks of men are of the 
most importance, in a hygienic point of view, both because 
we are constantly exposed to their influence, and because 
they are most completely subject to control. 

380. Their Relation to the Senses. — Many of these im- 
purities can be detected neither by taste nor smell, and are 
inhaled without any knowledge of their presence. Others 
are recognized at first ; but, as the nerves soon lose their 
delicate sensibility of discrimination, the senses are unre- 
liable monitors. Hence, injurious influences, that do not 
result in immediate and painful disease, are generally apt 
to be neglected. There is, besides, a false logic in the 
case, it being inferred that, because the senses lose their 






IMPURITIES OF THE AIR. 353 

susceptibility to morbific influences, the system therefore 
becomes accustomed and adapted to them, when they cease 
to be detrimental. Hut no error could be more pernicious, 
as it leads to carelessness and indifference with respect to 
those insidious agencies which slowly and silently sap the 
foundations of health. Common instinct is sufficient to 
guard against palpable causes of injury ; intelligence alone 
can protect us from the latent and deeper agencies of 
physiological mischief. 

381. Carbonic Acid as an Impurity. — Carbonic acid is 
thrown into the atmosphere by breathing, by combustion, 
and by the oxidation or decay of organic matter. A cubic 
foot of air, of average purity, contains a little less than a 
cubic inch of carbonic acid. A cubic foot of air, as it comes 
from the lungs, contains upwards of seventy cubic inches 
<»t carbonic acid. About three hundred and fifty cubic feet 
of air pass through the lungs of an adult man in twenty- 
four hours, losing some seventeen cubic feet of oxygen to 
the blood, and gaining therefrom a nearly equal quantity 
of carbonic acid. The breathing of each adult thus adds 
about one per cent, of carbonic acid to seventy-three cubic 
feel of air per hour, which would vitiate to this extent more 
than one foot per minute, while the effect is much increased 
by the surface exhalations. 

The quantity poured into the air by combustion is enor- 
ruous; fifteen thousand tons, according to the calculation 
<>f Dr. Angus Smith, arc daily thrown into the air from 
this source in the city of Manchester alone. But the prod- 

- of firing pass into the outer air, and, if gaseous, arc 

idly diffused ; but those of lighting, like those of breath- 
ing, an* often suffered to accumulate in living apartments. 
Tin* combustion of one cubic foot of coal-gas consumes the 

|Tgen of ten cubic feet of air. and produces two cubic 
of oarb >nic acid. The combustion of a pound of oil 

consumes the oxygen of one hundred and thirty feet of air, 

and produces ab >u1 twenty-one cubic feet of carbonic acid. 



354 ELEMENTARY HYGIENE. 

These facts show the rapidity with which the breathing 
medium of inhabited apartments tends to become dete- 
riorated. 

It is difficult to estimate the amount of carbonic acid 
arising from the decay of organic matter ; but, as such 
decay, under favorable conditions of temperature, is every- 
where going on, the daily aggregate must be very great. 
The increased quantity of carbonic acid found in the air 
of towns is doubtless partly derived from this source. 

As carbonic acid is constantly generated within the 
body, we may regard the presence of a certain small amount 
of it as quite compatible with health. But, when not 
promptly eliminated, its action becomes quickly injurious. 
Two volumes in a thousand of air cause headache and ver- 
tigo in many persons. Air containing one per cent, of it 
is soporific and depressing. From five to eight per cent, 
renders it dangerous to breathe, while ten to twelve per 
cent, makes it speedily destructive to life. 

The presence of an excess of carbonic acid in the air 
denotes in nearly every case a lessened proportion of 
oxygen, and, if the air has been contaminated by breath- 
ing, a decided increase in the amount of organic matter. 
These conditions make it dangerous to breathe ; but, 
w T hether this danger is due to the extra quantity of car- 
bonic acid and organic matter, or to the absence of oxy- 
gen, or partly to the one and partly to the other condition, 
is not yet clearly settled. It is sufficient for all practical 
purposes, however, to know that the three conditions are 
commonly associated in air contaminated by respiration. 

382. Watery Vapor as an Impurity. — When air enters 
the lungs its temperature is raised to nearly or quite that 
of the blood ; its capacity for moisture is thereby greatly 
increased, and when breathed out again it is always com- 
pletely saturated. Air in this condition, no matter what 
the source of its moisture, acts injuriously upon the sys- 
tem, as it is unable to further relieve the skin and lungs 



IMPURITIES OF THE AIR. 355 

of the watery vapor that is constantly seeking a means of 
escape. There follows the feeling of oppression and lan- 
guor which even the most robust often feel in close and 
sultry days. By this obstruction of insensible perspira- 
tion, not only an 1 the waste matters generated in the sys- 
tem unduly retained, but miasmas introduced through the 
lungs by respiration are prevented from escaping. This 
would lead us to expect a greater prevalence of epidemic 
diseases in moist than in dry districts, a fact observed in 
the case of cholera, which follows the banks of rivers, and 
revels in damp, low situations. Moisture, joined with 
warmth, has a relaxing and weakening influence upon the 
body. The debilitating effect of the sirocco upon the sys- 
tem, and its lowering and dispiriting influence upon the 
mind, are due to a heated atmosphere surcharged with 
moisture. Air, cold and damp, has a peculiarly chilling 
and penetrating effect, as illustrated by the east w T inds of 
spring in New England. 

383. Organic Matter. — This is a common impurity of 
the atmosphere, and is often present in dangerous propor- 
tions. It exists in the form of vapors and suspended mat- 
ters, and is found most abundantly diffused in the air of 
dwellings, hospitals, etc., and in the vicinity of decaying 

;mic substances. In health it is thrown off through the 
lungs by the process of respiration, and also by exhalation 
from the skin. The quantity has been estimated all the 
way from ten to two hundred and forty grains per diem 
for each adult. It varies, however, with the circumstances, 
the body excreting a much greater amount during a state 
of activity than when it is inactive, and more during dis- 

e than in a state of health. That coming from the lungs 

sista of an organic vapor, holding in suspension epithe- 
lium-cells that have heroine detached from the mucous sin- 
• the air-i 3, pharynx, mouth, etc. By the skin 

more is given out. Twice as much moisture leaves the 
body by thia route a- by the lungs, and it carries with it 



356 ELEMENTARY HYGIENE. 

into the atmosphere fatty matters, epidermic debris, and 
also small quantities of urea. 

This organic matter, when drawn through sulphuric 
acid, darkens it ; through permanganate of potash, de- 
colorizes it ; and through pure water, renders it offensive. 
It is probably in a state of combination with water, as the 
most hygroscopic substances, such as wool, feathers, and 
damp walls, absorb it in largest quantities. It has a pe- 
culiar, fetid smell, and on decomposition yields ammonia, 
being therefore nitrogenous. It is oxidized slowly, and is 
supposed to float through the air in clouds instead of un- 
dergoing rapid diffusion. The fetid odor of a bedroom in 
the morning, after it has been occupied during the uight, 
well attests the presence of these organic vapors. 

In the air of sick-rooms and hospitals organic matters 
accumulate in large quantities unless there is the most 
thorough ventilation. In addition to the amount con- 
tributed by respiration, which is often much larger in sick- 
ness than in health, the exhalations from the skin are 
greatly increased, and large quantities of effluvia also 
escape from the evacuations. Moscatti, who condensed 
the watery vapor of a hospital ward at Milan, describes it 
as being " slimy, and having a marshy smell." The dust 
of a ward in St. -Louis Hospital, in Paris, was discovered 
by Chalvert to contain, in one experiment, thirty-six per 
cent., and, in another, forty-six per cent, of organic matter, 
which consisted chiefly of epithelium, and when burned gave 
an odor of horn. An equal quantity was found in the plas- 
ter w r alls of the same ward. Pus-cells have been discovered 
in the air of an ophthalmic ward, and epithelium-cells are 
found in that of all ill-ventilated rooms. It is very likely 
that the specific poison of small-pox, scarlet fever, measles, 
diphtheria, etc., consists of molecular organic matter thrown 
off from the skin and mucous surfaces. If not rapidly oxi- 
dized, it no doubt retains its poisonous properties, and 
through the medium of the atmosphere conveys the dis- 



IMPURITIES OF THE AIR. 357 

ease. It is equally probable that the effluvia from cholera 
evacuations, through the medium of an impure atmosphere, 
propagate cholera. 

One part of carbonic acid in a thousand parts of re- 
spired air. indicates the presence of an amount of organic 
matter which, according to Dr. Partes, is perceptible to the 
senses and positively injurious to health. Smith, Wilson, 
and other equally competent observers, corroborate this 
view. 

384. Suspended Matters. — As shown by Tvndall, sus- 
pended matters in great variety are widely diffused. In 
the air of dwellings, starch-cells, hairs, fibres of cotton, 
wool, etc., are very common. In the air of towns, parti- 
cles of iron, stone-dust, and animal droppings, are also 
abundant, while the atmosphere generally contains spores, 
seeds, pollen, and broken- down vegetable tissue, together 
with the germs of vibriones, bacteria?, and other low forms 
of animal life. Many trades yield deleterious substances 
to the air in injurious quantities. These will be noticed 
in connection with the diseases which they commonly ex- 
cite. 

385. Contamination from Sewers and Cesspools. — Nbx- 
ious gases, entering the air from sewers and cesspools, 
consist mainly of carbonic acid, sulphuretted hydrogen, 
light carburetted hydrogen, sulphide of ammonium, and 
organic matter. They arise from the decomposition of or- 
ganic matter, and are yielded in large quantities, and at a 
rapid rate, when the temperature is high and the sewage 
concentrated. They are undoubted sources of disease, and 
are al-<> believed to be capable of conveying infectious 
matters, thus becoming, from their peculiar liability to 
enter houses, dangerous aids t<> the spread of epidemics. 
When distributed upon the land, unless greatly diluted, 
sewage gives off a disagreeable odor, and is the occasional 

Cause of diarrhoea and dysentery. 

386. Marsh Miasms. — Carbonic acid, light carburetted 



358 ELEMENTARY HYGIENE. 

hydrogen, sulphuretted hydrogen, and organic effluvia, con- 
taminate the air of marshes, which also abounds in vege- 
table matter and minute animal forms. Whatever the 
nature of the so-called miasm of marshes, we know that 
the air of these places frequently contains a something 
capable of producing the various forms of periodic disease. 
Exposure to marsh air also gives rise to diarrhoea, dysen- 
tery, and other forms of gastric disorder. Marsh diseases 
often follow the irrigation of meadows, draining of lakes, 
digging of canals, and excavation of railway-cuttings, and 
they are then ascribed to vitiation of the air from the 
decomposition of vegetable matter thus brought to the 
surface. 

387. The Cellar a Reservoir of Bad Air.— Confined air, 
without access of sunlight, soon becomes dank and un- 
wholesome. In the cellars of dwellings this is a common 
condition during a large part of the year ; the confined air 
is loaded with decomposing organic matter, given off from 
the masses of decaying vegetables with which cellars are 
stored. This foul air reaches the inhabitants of upper 
apartments in such small quantities as not usually to pro- 
duce any marked manifestation of disease, yet dangerous 
fevers have often arisen from neglect of cleanliness in this 
particular. 

Section III. — Morbid Effects of Impure Air. 

388. Its General Effects. — Besides the various diseases 
directly traceable to the influence of impure air, its effects 
are seen in a general depression of the tone of the system. 
Persons habitually occupying badly-ventilated apartments 
show this in pallor of countenance, depraved appetites, 
feeble digestion, and general w-eakness of body, and such 
are proverbially subject to attacks of acute disease. Dwell- 
ers in low situations, and in the vicinity of marshes, as 
well as those exposed to the poisonous emanations of 
sewers, and of decomposing organic matter, suffer in a 









MORBID EFFECTS OF IMPURE AIR. 359 

similar way, and this general impairment of the powers of 
the body is, doubtless, often the signal for the development 
of inherited taints that, under more favorable conditions, 

might lie dormant throughout a long and vigorous life. 
The incompleteness of nutrition gives >t length to the lurk- 
ing predisposition. Instances are constantly recurring in 
which consumptive tendencies are developed to a fatal 

issue through various bad conditions, impure air being the 
most common. And physicians are aware that the constant 
presence ot^ a pure atmosphere, with other means for healthy 
nutrition, will hold the predisposition in check, and main- 
tain the system above the plane of its influence. 

389. Consumption. — That breathing air already vitiated 
by respiration is a powerful aid in the production of con- 
sumption is acknowledged by all observers, and some go 
so far as to atfirm that this is its principal cause. The fact 
has been repeatedly noted that soldiers living in badly- 
ventilated barracks furnish a much larger percentage of 
consumptive cases than others who, in this respect, are 
comfortably housed. The same is true of sailors ; and the 
medical histories of operatives in close and overcrowded 
work-roorrs, both here and in foreign countries, abound 
with evidence of similar import. We have seen that re- 
spired air is deficient in oxygen, and contains an excess of 
• •arbonic acid, watery vapor, and organic matter. If it is 
breathed again, the blood immediately suffers both from lack 
of oxygen and from the accumulation of effete material. 
This condition r f the blood necessarily hinders the healthy 
waste and repair of the tissues, and must contribute to the 
formation of those depraved products which arc everywhere 

characteristic of consumption. The tubercles which in this 

make their appearance in the pulmonary organs 

Consist of crude, coagulated, half-Organized masses of albu- 
men, the abortive products of incomplete nutrition. And 
it seems but natural to expert that the organs with which 
the foreign ingredients of the atmosphere come more im- 



360 ELEMENTARY HYGIENE. 

mediately into contact, and the blood-vessels which they 
must enter on their passage into the system, should feel in 
a distinctive manner their noxious influence. 

Besides acting as a cause of consumption, impure air is 
a source of much suffering to those already diseased. The 
reason is obvious. The capacity of the lungs is more or 
less reduced, hence less air can be conveyed to the blood, 
and, if this is deficient in oxygen and contains impurities, 
the malady is directly aggravated. 

390. Scrofula. — That imperfect and perverted" state of 
the nutritive functions known as scrofula is the common 
attendant of life in a vitiated atmosphere. Baudoloque, 
an eminent French physician, declares that " the repeated 
respiration of the same atmosphere is a primary and ef- 
ficient cause of scrofula," and that " if there be entirely 
pure air, there may be bad food, bad clothing, and w r ant of 
personal cleanliness, but that scrofulous diseases cannot 
exist. . . . Invariably it will be found on examination that 
a trulv scrofulous disease is caused by a vitiated air, and it 
is not always necessary that there should have been a pro- 
longed stay in such an atmosphere. Often a few hours 
each day is sufficient, and it is thus that persons may live 
in the most healthy country, pass the greater part of the 
day in the open air, and yet become scrofulous, because of 
sleeping in a confined place where the air has not been re- 
newed." 

In 1832, at Norwood School, in England, where there 
were six hundred pupils, scrofula broke out extensively 
among the children and carried off great numbers. This 
was ascribed to bad and insufficient food. Dr. Arnott was 
employed to investigate the matter, and immediately de- 
cided that the food " was most abundant and good," as- 
signing " defective ventilation and consequent atmospheric 
impurity " as the true cause. 

391. Its Effects in Various Trades. — The most palpable 
examples of the injurious effects of breathing contaminated 



MORBID EFFECTS OF IMPURE AIR. 361 

air are furnished by the circumstances of certain industrial 
occupations. As a class the miners of England break down 
prematurely from bronchitis and pneumonia, caused by the 
atmosphere in which they live. The colliers of Durham 
and Northumberland, however, where the mines are well 
ventilated, do not appear to sutler from an excess of pul- 
monary disease. 

In the various trades, involving the inhalation of much 
dust by the workmen, bronchitis and its attendant disease, 
emphysema, are very common. In the pottery-trade, this 
malady occurs so frequently as to be known as the " pot- 
ter's asthma." Indeed, nearly all the flat-pressers and 

urers, according to Dr. Grenhow, eventually become 
asthmatical. Steel-grinders suffer terribly from inhaling 
the dust of their trade. The average duration of life, ac- 
cording to the statistics of Dr. Hall, of dry -grinders of forks 
is but twenty-nine years; razors, thirty-one years; scissors, 
thirty two years ; edge-tools, thirty-two years ; iiles, thirty- 
live years; saws and sickles, thirty-eight years. By the 
introduction of fans and wet-grinding, however, the danger 
has been materially reduced. Pearl-button makers are ex- 
tremely liable to pulmonary disease. Workers in ilax, and 
cot ton-wea vers, are equally exposed. Dr. Grenhow states 
that, of one hundred and seven flax-factory operatives, 
whose cases were taken indiscriminately, seventy-nine were 
Buffering from bronchial irritation, and in nineteen of these 
there had been haemoptysis. Among twenty-seven hack- 
lers, twenty-three were diseased The suspended particles 
drawn into the air-passages at each inhalation, and 
there find lodgment upon the delicate mucous surfaces with 
which they come in contact. The irritation thus set up 

• orbfl the working of the lungs, and, if maintained, event • 

ually ends in organic disease. 

Brass-founders, coppersmiths, plumbers, house-painters, 
white-lead manufacturers, match-makers, workers in mer- 
cury, are all subjed to peculiar forms of disease produced 



362 ELEMENTARY HYGIENE. 

by inhaling the fumes with which their business contami- 
nates the air. These fumes gain access to the blood, and, 
through this, to the whole system, producing severe local 
disturbance in many cases, and always affecting the gen- 
eral health. 

392. Diseases arising from Organic Impurities. — The 
effects of inhaling air vitiated by organic impurities are 
scarcely less apparent. Dr. Parkes says that he has known 
cases " in which the inhalation of such an atmosphere for 
three or four hours produced in men decided febrile symp- 
toms, increased temperature, quickened pulse, furred tongue, 
loss of appetite, and thirst, for even twenty-four or forty- 
eight hours subsequently."' Sewer-gas, the effluvia arising 
from decomposing animal matter, the emanations from 
manure-manufactories and bone-boiling establishments, all 
contain organic matter, and are all prolific sources of dis- 
ease. Diarrhoea and dysentery are the most common af- 
fections which spring from these causes ; but enteric, or 
typhoid fever, is held by Dr. Murchison to be produced in 
a similar way, sewer-air being especially dangerous. Much 
uncertainty prevails as to the real cause of this disease, but 
modern investigators incline to the belief that it is infec- 
tious, and that it is propagated by the distribution of or- 
ganic matter in water and air. " I readily admit," says 
Dr. Murchison, " that we cannot succeed in tracing every 
case of enteric fever to organic impurities ; but, if the dis- 
ease can be traced to such causes in a few undoubted in- 
stances, it is reasonable to infer that its causes are similar 
in all cases where it has a spontaneous origin. As already 
stated, the actual poison may, like the miasmata which give 
rise to ague, be inappreciable to the senses, or by chemical 
research. During the last four years, however, I have met 
with few examples of enteric fever which, on investigation, 
I could not trace to defective drainage, the existence of 
which was occasionally unknown to the inhabitants of the 
infected locality." 



MORBID EFFECTS OF IMPURE AIR. 363 

That the spread of cholera is also due to some specific 
organic poison is rendered probable by the feet that, where 
water and air are kept free from organic impurities, the 
disease is unable to gain a foothold. 

393. Effects of Impure Air on the Course of Disease.— 
Foul air increases the severity of disease, rendering a fatal 
result much more probable, and, even if this is avoided, 
greatly prolongs the period of convalescence. It also pre- 
disposes to complications, and renders recovery more likely 
to be followed by subsequent trouble. This appears to hold 
true of all diseases, but especially of the febrile. It is 
known that, in the treatment of typhus and typhoid fevers, 
the freest ventilation, even to the extent of placing the 
patient in the open air, reduces the mortality more than 
half, and greatly shortens the time of recovery. A like 
provision in the treatment of scarlet fever, measles, small- 
pox, diphtheria, etc., not only renders them much less 
severe, but does away in a great degree with the neces- 
sity for medication, and also markedly diminishes the lia- 
bility to those distressing sequelae which, in less favorable 
conditions, so often supervene. 

394. Effects of the Air of Sick-Rooms. — The impurities 
of a sick-room atmosphere consist largely of organic mat- 
ter, which not unfrequently bears the specific poison of the 
disease. This is the case with the exanthemata, as well 
a- with other contagious febrile affections. On uncovering 

•arlet-fever patient in the direct rays of the sun, a cloud 

of fine dust may be seen to rise from the b( dy — contagious 

- T . that in unventilated localities is but simvh- dispersed 

destroyed, and that may for days retain its poisonous 

qualities. Diseases of this charact* r are undoubtedly prop- 

_ ted in other ways, but a confined atmosphere probably 

- more than all other causes put together towards aiding 
their diffusion* The spread of erysipelas and gangrene in 
the Burgical wards of hospitals, and the propagation of 
purulent ophthalmia, observed in some of the London 



364 ELEMENTARY HYGIENE. 

charit} T schools, take place through the medium of the 
atmosphere, which becomes highly charged with the ema- 
nations from the sick. Besides bearing the specific poison, 
an atmosphere of this character is exceedingly depressing 
to those brought within the range of its influence, and, by 
thus lessening the resisting power of the system, renders 
the otherwise healthy liable to attack. 

395. Morbid Mental Effects of Bad Air. — Breathing an 
impure atmosphere injures the mind as well as the body. 
If the blood which is sent from the lungs to the rest of the 
system is imperfectly aerated, no organ feels it more than 
the brain. Its immediate effect is to cloud the mind and 
depress its energy; sharpness of attention, clearness of ap- 
prehension, and readiness of memory, are all impaired. 
" The health of the mental and bodily functions, the spirit, 
temper, disposition, the correctness of the judgment, and 
brilliancy of the imagination, depend directly upon pure 
air." 

Dr. Ray remarks: u In a school, or hospital, or other 
considerable assemblage of people, the purity of the air 
may be pretty accurately measured by the amount of cheer- 
fulness, activity, and lively interest, which pervades it ; and 
yet so little do people think or care about this subject, that, 
under existing arrangements, there are very few who do 
not every day of their lives inspire more or less highly- 
vitiated air. The listlessness and stupidity of students, 
and especially of children confined in the school-room, are 
often due to the bad state of the air they breathe. Using 
the brain in a vitiated atmosphere is like working with a 
blunted instrument, and the effect, of course, must be ag- 
gravated where the inexperienced are first learning the use 
of the instrument. 

Section IV. — Purification of the Air. 

396. Nature's Resources. — The purification of the gen- 
eral atmosphere is maintained by various agencies. By 



PURIFICATION OF THE AIR. 365 

the law of diffusion all gases intermingle, so that where 
impurities are sen free at any point they tend to exhale, or 
diffuse away, and thus become weakened and lost in the 
great body o( the atmosphere. The mixture of large masses 
of air and the dispersion and dilution of local impurities 
are also effected by the winds. Gaseous exhalations are 
washed out and absorbed from the atmosphere by the fall 
of rains. The earth's vegetation destroys carbonic acid, 
while the oxygen slowly burns up the numberless combus- 
tible vapors and contaminations which are thrown into the 
air. By these means the earth's atmosphere is constantly 
maintained respirable and pure. 

397. Ventilation. — Taking the fresh external air as the 
standard of purity required for health, the object of ven- 
tilation is to conduct it through dwellings, hospitals, work- 
shops, and places of similar character, in a manner that, 
without inconvenience to the inmates, shall accomplish the 
rapid and thorough dilution and removal of whatever im- 
purities their atmosphere may contain. To do this effect- 
ually, and without risk to the health and comfort of the 
persons present, the ventilation must conform to certain 
indispensable conditions: 

(1.) The air which enters must itself he jmre. This 
may generally be secured by taking it from almost any 
exposed situation, unless there be some special source of 
impurity in close proximity. It is desirable, if possible, 
particularly in cities, to introduce the air from a level a 
few feel above the surface, as there are more or less ex- 
halations constantly floating in air next the ground. 

(2.) It must be in sufficient </><<i,,t;t>/. We find Na- 
ture's standard of purity in the external atmosphere, and, 
other I jiial. the nearer we approach this in our 

dwellings, the healthier will be their inmates. The earlier 
authorities on ventilation varied greatly in their estimates 
of the quantity necessary, some placing it as low as sixty 
cubic feet per head per hour, while others considered live 



366 ELEMENTARY HYGIENE. 

hundred cubic feet as not too much. More thorough in- 
vestigations have since been made, and it is found that 
even the highest of these estimates is quite insufficient. 
Dr. Parkes says : " From a number of experiments in which 
the outflow of air was measured, and the carbonic acid 
simultaneously determined, I have found at least tw^o thou- 
sand cubic feet per hour must be given to keep the carbonic 
acid at five or six per one thousand volumes, and to entirely 
remove the fetid smell of organic matter." Nothing less 
than this can be tolerated without risk to health, and it is 
found that a much larger allowance is productive of the 
best results. It has been stated, from extensive observa- 
tions, that in mines, if it be wished to keep up the greatest 
energy of the men, no less than one hundred cubic feet per 
man per minute (= six thousand cubic feet per hour) must 
be given. If the quantity is reduced to one-third, or even 
one-half, there is a decided diminution in the amount of 
work performed. 

If possible, the supply for the sick should be unlimited. 
In some diseases, so much organic matter is thrown off, 
that scarcely any ventilation is sufficient to remove the 
odor. Such diseases as pyaemia, typhus and typhoid fevers, 
small-pox, and the like, are best treated in the open air. 
This is found of the utmost value, more important even 
than diet and medicines. Grassi mentions that the air in 
a ward in the Hopital Necker, in Paris, was perceptibly 
tainted by emanations from a cancerous ulcer, although 
the ventilation at the time was thirty-five hundred cubic 
feet per head per hour. 

(3.) Its movement must be imperceptible. Air may 
move at the rate of one hundred feet per minute without 
violating this requirement ; but this is a much greater ve- 
locity than is needed for ventilating purposes — that is to 
say, after the air has once entered the apartment. In the 
flues, the rate of movement is of little consequence, except 
that it be sufficiently rapid to afford the required supply. If 



PURIFICATION OF THE AIR. 367 

there is little or no interference from outside currents, the 
air within the building may readily be made to move in a 
body from above downwards, and the rapidity of its move- 
ment can be easily regulated It may be objected to this 
downward movement that the impurities naturally tend 
upwards, with the course of the warmer air, and that, by 
being made to take a downward direction, they are brought 
back again to be reinhaled. If it were true that the im- 
purities, as such, immediately rose to the ceiling and 
escaped from the apartment, the objection would hold ; 
but this is not the case. On the contrary, it is known thai 
the carbonic acid and other gaseous impurities are equally 
diffused, and the weight of the organic substances and 
other suspended matters leads to the inference that they 
would gravitate towards the floor, particularly when rising 
currents of warm air are excluded, as they should be, by 
introducing it at the top of the room. In no other way 
can so steady and equable a movement be obtained as by 
introducing the warm air at the top and removing it be- 
low ; and, apart from any theoretical considerations, it is 
found to yield excellent practical results. 

(4-.) Its temperature must be suitably regulated. In 
this climate, cooling the air is rarely necessary, but in the 
colder months of the year the incoming air requires to be 
warmed sufficiently for comfort, and in such manner as not 
to disturb the normal proportions of its constituents. The 

it danger i- that of overheating it, whereby its capacity 
for moisture is greatly increased and ventilation becomes 
converted into a kiln-drying process scarcely less injurious 
than impure air. The policy BDOllld be to introduce large 
quantities of air raised only to a proper breathing tempera- 
ture (60 t<. 1«> F;ihr. ). the temperature to be maintained 
by a steady and rapid change, so directed as to remove the 

ler air of the apartment, and replace it with that freshly 

warmed. It may be Baid that this involves a much greater 

u of heat than the opposite course, viz., raising t 



368 ELEMENTAKY HYGIENE. 

high temperature smaller quantities of air. Even if this 
were true, which is not the case, waste of heat would be 
far preferable to the loss of health, which the latter pro- 
cess involves, both by the increased drying power it gives 
the air, and by insufficient ventilation. 

The heat imparted to the air in this process becomes a 
means of promoting its movement. With this as a motive 
power, by the aid of flues and ventilating shafts, very 
thorough purification may be obtained. 

398. Artificial Purification— Disinfectants. — In certain 
special cases where the air is being rapidly contaminated 
by foul or poisonous exhalations, and where, either from 
confinement or other cause, the purifying agencies of Na- 
ture are unable to w^ork with sufficient rapidity and vigor, 
recourse is had to various artificial means of purification, 
with a view to the immediate destruction of such emana- 
tions. The more common and useful of these are heat, 
charcoal, chlorine, carbolic, nitrous, and sulphurous acids, 
sulphate of iron (copperas), Condy's fluid, and chloralum. 

Seat is highly commended as a means of destroying 
animal and vegetable germs, and infectious matters. It is 
especially valuable for the disinfection of clothing, bedding, 
and the like, where it can be confined, but is not so readily 
applicable for cleansing the air. To be effective, a heat 
of at least 140° Fahr. is required; 160° or 180° Fahr. is 
even more certain, and may be applied without risk to the 
fabric. 

Charcoal presents an immense absorbent surface to the 
air, a cubic inch of beech wood-coal equaling in surface one 
hundred square feat (Liebig). It is therefore a powerful 
oxidizer of organic matter, catching and holding the par- 
ticles in contact with oxygen, already within it, until their 
destruction is accomplished. Its effects are especially 
marked with sewage-gases, and with the organic emana- 
tions in disease. Of the different kinds, animal charcoal is 
regarded as best for disinfecting purposes. 



PURIFICATION OF THE AIR. 369 

Chlorine decomposes sulphuretted hydrogen and sul- 
phide of ammonium, and also destroys organic odors. It 
is an energetic aerial disinfectant, but, owing to its irritat- 
ing effect on the lungs, requires to be used in small quan- 
tities, or in uninhabited rooms. It may be easily obtained 
by mixing one pari of powdered binoxide of manganese 
with four parts of common salt and four of dilute sulphuric 
acid. A gentle heal will aid the evolution of the gas. 
Various compounds of chlorine are often employed for dis- 
infecting purposes, hut all owe their value to the presence 
of this element. Chlorides of lime and soda yield it in 
small quantities when moistened with water. Chloralum 
is a compound of chlorine and aluminium, but thus com- 
bined the chlorine is not volatile; the preparation is, there- 
fore, of little value for purifying the air. Applied to de- 
composing organic matter, however, it acts as an excellent 
deodorant, arrests putrefactive change, and at once puts a 
M<>p to the development of animalcuhe. In solution it is 
very useful for washing infected clothing, and for cleansing 
the walls and wood-work of sick-rooms. 

t 'arbolic acid is a powerful antiseptic and disinfectant. 
It arrests all kinds of putrefactive change, and quickly de- 
stroys animal and vegetable germs, and the low forms 
of life. Being also an excellent deodorant, it is used ex- 
tensively for disinfecting the vessels of sick-rooms, urinals, 

bles, manure-heaps, and cesspools. The commercial 
form is a dark-brown tarry liquid, with the pungent odor 
of creosote. It is highly poisonous, and hence requires to 
be used with care. 

Nitrous acid may be evolved by placing nitre in sul- 
phuric acid, or by dropping a bit of copper into dilute 
nitric acid. It i- ;< very efficient disinfecting agent, but 
irritating to the air-passages and lungs. The ease with 
which it yield- up ;i portion of Its oxygen makes it a pow- 

il oxidizer, which acts rapidly upon organic emanations. 

Sulphurous acid is given off when sulphur is burned. 



370 ELEMENTARY HYGIENE. 

It decomposes sulphuretted hydrogen, and acts with energy 
upon organic substances. 

Sulphate of iron is chiefly valuable for disinfecting 
sewage, privy-vaults, manure-heaps, and cesspools, where 
it is desired to arrest decomposition, and the generation 
of foul odors. 

Permanganate of potash, or soda ( Concfys fluid), 
gives off oxygen, and rapidly destroys organic matter. 
Ammoniacal compounds are at once decomposed. Per- 
manganate of soda, taken into the mouth, quickly destroys 
the odor of tobacco (Hoffman). 



CHAPTER XVI. 

WATER AND HEALTH. 

Section I. — Physiological Offices of Water. 

399. Amount in the Body. — The student is aware that 
water is a very large constituent of all parts of the body. 
The bones contain 130 parts of it in 1,000; muscle, 750; 
brain, 789 ; blood, 795 ; and it forms nearly three-fourths 
the entire weight of the body. 

400. It is the Instrument of Change. — Water gives full- 
ness and flexibility to the softer tissues, and is the great 
agent of movement within the system. It performs the 
same office of transportation and exchange in the vital 
economy that it does by oceans, rivers, and canals, in the 
commerce of the world. Nutritive substances cannot enter 
the system, nor the debris of the tissues leave it, except in 
a state of solution ; it is the office of water to bring them 
into this condition, and convey them to their various places 
of destination. 

401. Its Solvent Power.— Water performs these duties 
by virtue of its remarkable powers as a solvent. Perfectly 



PHYSIOLOGICAL OFFICES OF WATER. 371 

neutral itself, it becomes sweet, sour, salt, astringent, bit- 
ter, or poisonous, accordingly as the bodies it dissolves 
possess these properties. It readily takes up either gase- 
ous, liquid, or solid substances, and thus becomes a means 
for their rapid ami wide-spread diffusion. 

402. Quantity daily taken. — Water is taken not only 
in the form of drink, but it is a large constituent of the 
various food-stufls; hence any estimate of the quantity 
passing into the system, to be reliable, must include both 
these sources ^\ supply. It has been found thai a healthy 
adult man ordinarily takes from seventy to ninety ounces 
in twenty-four hours. The amount, however, varies greatly 
in different circumstances, sometimes, from individual pe- 
culiarities, falling much below, and at other times consider- 
ably exceeding this figure. 

403. Its Excretion. — Water is constantly escaping from 
the system, either in a fluid or vaporized form, and carries 
with it the various substances resulting from the wear and 
tear of the tissues. Of all that is expelled, about forty- 
eight per cent, is discharged with the mine and faeces, and 
a!> mt fifty-two per cent, by the lungs and skin. Of the lat- 
ter, the skin discharges nearly twice as much as the lungs. 

Section II. — Different Kinds of Water. 

401 Its Foreign Ingredients. — Owing to its extraordi- 
y solvent power, water, in a natural condition, is never 
found free from foreign ingredients, which modify its char- 
acter according to the quantity present, and their own 
p iculiar properties. This gives rise to the several varieties 
i we km ft water, hard water, mineral water, and 

•water. 

405. Soft Water. — This is water thai gives a feeling of 

ness m washing, from the absence of certain mineral 

. which render it rough of hard. Rain-water 

may be taken as a fair example, for, when caught in the 

•untrv-. it is the purest water thai Nature provides. 



372 ELEMENTARY HYGIENE. 

It is not entirely free from foreign matters, however, for, 
as it falls through the air, it absorbs oxygen, nitrogen, 
carbonic acid, ammonia, and organic substances, and also 
washes out any impurities which the atmosphere may 
happen to contain. Thus, in the vicinity of the ocean the 
air contains traces of common salt ; in the neighborhood 
of ciiies, various saline, organic, and gaseous impurities, 
while dust is raised from the ground and scattered through 
it by winds. These are all rinsed out by rain. In passing 
through the air water becomes highly aerated ; that is, ac- 
quires an atmosphere of its own, which contains from ten 
to fifteen per cent, more oxygen than ordinary air. This 
gives to water its agreeable taste. 

Soft water, which is free from dissolved mineral mat- 
ters, makes its way into organized tissues with much greater 
readiness than hard water. It also exerts a more powerful 
solvent or extractive action, and is thus a better vehicle 
for conveying alimentary substances into the living system. 
In culinary operations, where the object is to soften the 
texture of animal and vegetable substances, or to extract 
from them and present in a liquid form some of their valu- 
able parts, as in making soups, broths, stews, or infusions, 
as tea and coffee, soft water is much to be preferred. 

In consequence of its aeration, rain-water is both healthy 
and pleasant as a beverage. The greatest benefits have re- 
sulted in many cases from its use, where the spring and 
well waters were largely impregnated with earthy salts. 

406. Hard Water. — Rain-water, as it penetrates the 
ground, absorbs a large proportion of carbonic acid from 
the air in the interstices of the soil, which is two hundred 
and fifty times richer in this gas than the air above. The 
presence of this absorbed carbonic acid greatly increases 
the solvent power of water upon mineral substances. Pass- 
ing more or less deeply into the earth, it dissolves many sub- 
stances which it meets ; hence the difference between spring 
and well waters, which are generally hard, and rain-water, 



DIFFERENT KINDS OF WATER 373 

which has not come in contact with the ground The life 
and sparkle of spring and well water are due to the pres- 
ence of carbonic acid thus taken up, and, when this is found 
in a considerable degree, it is safe to infer the additional 
presence of large quantities of saline matter. The usual 
ingredients of well and spring water are lime, magnesia, 
soda, and oxide of iron, combined with carbonic and sul- 
phuric acids, which form carbonates and sulphates. Com- 
mon salt is also often present. The most usual ingredients, 
however, are carbonate and sulphate of lime. Carbonate 
of lime, or limestone, is not soluble in pure water, but dis- 
solves in water containing free carbonic acid. 

The amount of mineral matter found in water varies 
greatly. The water of the river Loka, in Sweden, which 
flows over insoluble granite, contains only ^th of a grain 
of mineral matter in an imperial gallon. Common well 
and spring waters contain from five to seventy grains per 
gallon. Sea-water contains twenty-six hundred prains to 
the gallon; and that from some parts of the Dead Sea, or 
the Great Salt Lake of Utah, as much as twenty thousand 
grains to the gallon. 

Mineral waters are usually those of springs which are 
highly charged with one or more mineral ingredients. 
Those abounding in salts of iron are called chalybeate 
waters. If the waters are brisk and sparkling, carbonic 
acid is present, and they are termed carbotwtiedj or acidu- 
lous. 

IA\ -waters are also clear, sparkling, and agree- 

able to the taste. They differ from the water of chalk 
districts, in containing more sulphate of lime and lc>> car- 
bonate, and in dolomitic districts much sulphate and car- 
bonate of magnesia. They contain little organic matter, 
but are very hard, soften little on boiling, and are gener- 
ally unwholesome. 

Sand and gravel unxters vary in character in different 
regions. Some are v<tv pure, containing less than five 



374 ELEMENTARY HYGIENE. 

grains of mineral matter in a gallon, and less than one 
grain of organic matter. Others again, particularly such 
as flow over soft sand-rock, are liable to be very impure, 
containing much chloride of sodium, carbonate of soda, iron, 
and a little lime and magnesia, amounting altogether to 
from thirty to eighty grains per gallon. The organic mat- 
ter may also be in large amount, from four to ten grains 
per gallon, or even more. 

Alluvial waters, as a rule, are highly charged with car- 
bonate of lime, sulphate of lime, sulphate of magnesia, 
chloride of sodium, carbonate of soda, iron, silica, and often 
with organic matter. The amount of solids per gallon 
ranges from twenty to one hundred and twenty grains. 

Surface and subsoil water is often very impure. Cul- 
tivated lands, with rich, manured soils, furnish a water 
often containing both organic matter and salts in large 
quantity. In towns, and among the habitations of men, 
the surface and shallow well water frequently contains 
large quantities of nitrites and nitrates, sulphates and 
phosphates of lime, and soda and chloride of sodium. Or- 
ganic matter, also, exists often in large amount. 

Marsh-water is always impure from the presence of 
much organic matter, which is chiefly of vegetable origin, 
and varies in quantity from ten to fifty grains in the gal- 
lon. The proportion of mineral ingredients is usually 
small, unless the marsh be salt, when the mineral con- 
stituents of sea-water are present. 

River-water varies much in the number and quantity 
of its constituents. Coming from various sources, it is 
even more complex in constitution than spring or well 
water. Oftentimes it is greatly contaminated by the sew- 
age of towns, and the refuse of manufacturing operations, 
which are carried on along its banks, and it is also likely 
to contain a large amount of organic matter. 

Sea- Water. —The solid constituents of sea-water amount 
to about three and a half per cent, of its weight, or nearly 



DIFFERENT KINDS OF WATER 3 75 

half an ounce to the pound. It is unfit for use unless dis- 
tilled. It then answers well for cooking purposes, and, if 
thoroughly aerated, is palatable. Any organic matter re- 
maining after distillation may be removed, by passing the 
water through a charcoal filter, or by letting it stand for a 
few days. Care should be taken that no lead finds its way 
into distilled water, as it is rapidly taken up. Many cases 
of lead-poisoning have occurred on board ships, partly from 
the use of minium in the apparatus, and partly from the 
use of zinc pipes, with lead in their composition. 

407. Purity of Water.— Perfectly pure water can only 
be obtained by the most careful processes of distillation, 
and is never found as such in a natural state. Hence the 
difficulty of defining what are properly impurities, particu- 
larly when we remember that water containing consider- 
able quantities of foreign matter may be used for long 
periods together, without producing any recognizably in- 
jurious results. Experience has shown, however, that cer- 
tain conditions are necessary to health, and cannot be 
neglected with impunity. The water should be transparent 
and colorless, free from odor, and without taste. It should 
also be well aerated, and afford no deposit on standing; 
above all, it should be free from organic matter. Probably 
the less it contains of saline ingredients the better. The 
Sanitary Congress held at Brussels, in 1853, decided that 
the total amount ought not to exceed eighty-live grains 
per gallon. But this furnishes no reliable criterion, as a 
far less quantity of sulphate of lime, or magnesia, is known 
to be injurious, while the proportion of carbonate of lime, 
or soda, may considerably exceed this, and produce no 
manifestly bad effects. 

408. Organic Impurities in Water. — These vary exceed- 
ingly in character and amount, and may be either mechani- 
cally suspended, or dissolved in the water. If suspended, 
and of vegetable origin, their presence will often be indi- 
cated by a peculiar yellowish or brownish tinge, such as 



376 ELEMENTARY HYGIENE. 

most are familiar with in the water of marshes or peat-bogs. 
If of animal origin, they may impart no tinge, and are more 
likely to be dissolved. They are derived from numberless 
sources, but those of most importance, hygienically, are 
furnished by the habitations and trades of men. Rain- 
water carries down from the air floating organic impuri- 
ties, and it may also become contaminated by decaying 
leaves that have accumulated on the roofs of houses. Cis- 
terns are also liable to receive impurities from the leaking 
of sinks or waste-pipes, or by the washing in of leaves from 
the roof. Shallow wells are extremely apt to become con- 
taminated by floods carrying in organic surface impurities. 
Deep wells frequently drain large areas about them, and 
are very often, particularly in towns, rendered impure and 
even offensive by collecting the drainage from cesspools, 
vaults, etc. In epidemics of typhus and typhoid fever and 
cholera, cases have occurred where it was known that the 
specific poison of the disease found its way into the system 
by this means. Springs and streams oftentimes receive 
the discharges from large manufactories ; and, although 
the water appears pure, an examination reveals the pres- 
ence of organic matter. The effects of this contamination 
may be shown by taking a little of the sediment that has 
accumulated at the bottom of a cistern, and placing it in a 
bottle of perfectly pure distilled water, when, in a short 
time, if the w^eather be warm, it will smell offensively. 
Thus, at ordinary summer temperatures, this organic mat- 
ter is liable to undergo putrefactive change, and it is then 
that it exerts its most baneful effects upon the system. 
This, no doubt, is one of the causes of the greater preva- 
lence of diarrhoeas and dysenteries during the warmer por- 
tions of the year. 

409. Action of Water on Lead. — Water is known to 
possess the power of corroding lead, and forming com- 
pounds with it which, if dissolved, render the water highly 
poisonous. All waters act upon it more or less, but it is 



DIFFERENT KINDS OF WATER. 377 

only when the lead is dissolved that the water containing 
it becomes dangerous. When ordinary water is placed in 
contact with lead, the free oxygen it contains combines 
with the metal, forming oxide of lead, with which the 
water immediately unites, producing hydrated oxide of 
lead, which is nearly insoluble. There is also more or less 
carbonic 1 acid existing in all natural waters ; this combines 
with the oxide of lead, forming carbonate of lead, which 
is also highly insoluble. But, if there be in the water 
much carbonic acid, a bicarbonate of lead is formed, which 
is very soluble, and therefore remains dissolved in the 
water. Hence, waters which abound in free carbonic acid, 
as also those which contain bicarbonates of lime, magnesia, 
and potash, are most liable to become poisoned by lead. 
Water containing common salt acts upon the metal, form- 
ing a soluble poisonous chloride of lead. The presence 
of organic matter, nitrites and nitrates, imparts to the 
water a powerfully-corrosive action. If the water contains 
vegetable or fatty acids of any kind, or sour milk, or cider, 
its action on lead is greatly increased, and it is more like- 
ly to dissolve the compounds formed. On the other hand, 
waters containing sulphates and phosphates are little in- 
jured, these silts exerting a protective influence on the 
lead. 

The lead itself is more easily acted upon if other metals, 
such as iron, zinc, or tin, are in contact with it. Galvanic 
action is set up, which greatly facilitates corrosion. 

Dr. Hassal says that, " while very soft water cannot be 

stored for a lengthened period, with impunity, in leaden 

ssels, the danger of the storage of hard water, under the 

le circumstances, is in most cases much greater. This 
danger, however, is to be estimated neither by the qualities 
of hardness or softness, but altogether depends upon the 
chemical constitution of each different kind of water. Thus. 
if this be ever SO soft, and contain Ucc carbonic acid, its 
iCtion on lead will be greal j whereas, if it be hard from 



378 ELEMENTARY HYGIENE. 

the presence of sulphates and phosphates principally, and 
contain but few bicarbonates, little or no solution of the 
lead will result." 

Section III. — Morbid Effects of Impure Water. 

410. Dyspepsia. — Water containing sulphate of lime, 
chloride of calcium, and the magnesia salts, has a decided 
tendency to produce stomachic and intestinal derangements. 
Dr. Sutherland found that the hard water of the sandstone 
rocks, which was formerly much used in Liverpool, exerted 
a marked effect in producing constipation, lessening the 
secretions, and causing visceral obstructions ; and, in Glas- 
gow, the substitution of soft for hard water, according to 
Dr. Leech, lessened the prevalence of dyspeptic complaints. 
The exact amount capable of producing these symptoms 
has not been determined. In a well-water which was found 
so injurious that men would not drink it, there were pres- 
ent nineteen grains of carbonate of lime, eleven grains of 
sulphate of lime, and thirteen grains of chloride of sodium 
per gallon. The total solids were fifty grains per gallon. 
Iron, in quantities sufficient to give the water a slightly- 
ferruginous taste, often produces dyspepsia, headache, and 
general uneasiness. 

411. Diarrhoea. — That this disease often originates in 
the use of bad water, there is no doubt. Great numbers 
of instances are on record where it was traced directly to 
this cause, and where a change of water was followed by a 
disappearance of the disease. 

Mineral matters, either dissolved or suspended, will 
give rise to it if present in considerable quantity. The 
w r ater of many rivers holds in suspension fine particles of 
clay or marl in great abundance, particularly at certain 
seasons, and, if drunk for any length of time, will produce 
diarrhoea. The use of waters containing dissolved mineral 
substances, particularly sulphates, will also cause diarrhoea. 
" Parent Duchatelet noticed the constant excess of patients 



MORBID EFFECTS OF IMPURE WATER. 379 

furnished by the prison of St.-Lazare, in consequence of 
diarrhoea, and he traced this to the water, which 'con- 
tained a very large proportion of sulphate of lime and 
other purgative salts'" (Parkes). Waters impregnated 
with nitrate of lime will produce diarrhoea. Brackish 
water arts in the same way, probably from the large quan- 
tity of chloride of sodium it contains. 

Dissolved or suspended organic matter, whether of 
getable or animal origin, will cause diarrhoea. In the 
recent war, great numbers of cases occurred from the use 
of marsh or ditch water; the sickness ceased when wells 
were sunk. Water containing fecal matter, sulphuretted 
hydrogen, or other sewage products, often occasions the 
worst forms of diarrhoea, attended sometimes with marked 
choleraic symptoms — such as purging, vomiting, and 
cramps — even when the senses give no indication of these 
impurities. 

The effects of sulphuretted hydrogen are well shown 
by a case that occurred in the late war in Mexico. The 

inch troops suffered greatly at Orizaba, from the use 
of water taken from sulphurous and alkaline springs. r lhis 
produced dyspepsia and diarrhoea, attended with enor- 
mous eructations after meals, the eructed gas having a 

>ng smell of sulphuretted hydrogen. Sewage-gases, 

ting back through untrapped overflow-pipes into tanks 
and cisterns, often contaminate the water very rapidly. 

412. Dysentery. — This also frequently results from the 
of impure water. The impurities which produce it 

appear to be of the same kind as those which cause di- 
arrhoea. The drainage from graveyards contains large 
quantities of organic matter and nitrates, and its use IS 

very liable to produce this disease. Water contaminated 

by the discharges of dysenteric patient- i- known to pro- 
due- dysentery in others, and thus the disease oftentimes 
►mea epidemic. 

413, Cholera. — Symptoms of this malady often follow 



380 ELEMENTARY HYGIENE. 

the use of water containing sewage or decomposing or- 
ganic matter. Many believe that such water is capable 
of producing the disease, but this point is still unsettled. 
There is any amount of evidence, however, that the dis- 
ease is frequently conveyed in drinking-waters which have 
been tainted with cholera-evacuations. It is also quite 
certain that the use of impure water of any kind predis- 
poses to cholera. It probably acts by keeping up a con- 
stant irritation in the alimentary canal, thus causing diar- 
rhoea, which in cholera epidemics usually precedes the 
outbreak of the graver disease. 

414. Enteric Fever. — The spread of this disease has of 
late years been frequently traced to the agency of drinking- 
waters contaminated either with decomposing organic mat- 
ter, or the discharges of fever-patients. The most usual 
condition of its outbreak is the use of water from wells or 
reservoirs that receive the soakage from defective drains, 
from privy-vaults, or from some other contiguous source of 
filth. The instances of its originating in this way are 
too numerous, and have been too clearl}- traced, to admit 
of a doubt of the fact, nor does mere dilution of the 
poison remove the danger, as the following will show : A 
recent outbreak in an English town was traced to the milk 
with which numerous families were served, and it was con- 
clusively proved that this milk was poisoned by being 
stored in cans that had been washed with water contami- 
nated with sewage from an imperfect drain. 

415. Malarious Fevers. — There is strong evidence in 
support of the belief that these are often produced by 
drinking marsh or ditch water. They are supposed to be 
caused by some specific poison generated in marshy re- 
gions ; and that this may find its way into the blood 
through the agency of water, as well as of air, there is no 
reason to doubt. Mr. Blower, of Bedford, England, men- 
tions a case in which, in the parish of Houghton, almost 
the only family which escaped ague at one time was that 



PURIFICATION OF WATER. 381 

of a farmer who used well-water, while all the other in- 
habitants drank ditch-water. 

In yellow fever, like dysentery, typhoid fever, and 
cholera, the alimentary mucous membrane is primarily af- 
fected.. Hence, there is strong probability that the cause 
IS also swallowed in this ease, and outers with the drink- 
ing-water. 

416. Goitre, or enlargement of the thyroid gland, is 
most common in limestone regions, and is held by some to 
be caused by drinking- water highly impregnated with lime 
and magnesia salts. Johnston states that in the jail at 
Durham. England, when the water contained seventy-seven 
grains per gallon of lime and magnesia salts, all the pris- 
oners had swellings of the neck. These disappeared when 
a purer water, containing eighteen grains per gallon, was 
obtained. 

417. Entozoa, or those parasitical creatures which in- 
fest other animals, may-find their way into the body by 
means of the drinking-water. While some enter with the 

1, others (in the embryo state) are known to exist in 
it numbers in river-water, and doubtless are often swal- 
lowed when such water is used for drinking purposes. 

Section IV. — Purification of Water. 

418. Examination by the Senses, — If water is examined 
by the unaided senses, the information obtained i- \<'vy 
limited and should not be relied upon. They will only 
indicate extreme conditions, and are very liable to overlook 
the most characteristic impurities. Taste, for instance, 

n though it be extremely delicate, is wholly untrust- 
worthy. Organic matter, when dissolved, is often quite 
g tins of carbonate of soda and 70 of chloride 
of sodium per gallon are imperceptible; 16 grains of car* 
of lime L r iv<- n and 25 grains of sulphate 

of lime very little. If, from it- effects, a given watei 

ted of impurity, and Cannot be avoided, e\- 



382 ELEMENTARY HYGIENE. 

amination of it should be intrusted to some competent 
person. 

419. Distillation. — Water may be most thoroughly puri- 
fied by distillation, but this is impracticable when consid- 
erable quantities are required, and, besides, the water is not 
tit to drink until aerated. To render it perfectly pure, it 
must be redistilled at low temperatures, in silver vessels. 

420. Boiling and Freezing.— Boiling kills most animal 
and vegetable organisms that water may contain, expels 
gases, and precipitates carbonate of lime. It is the latter 
that constitutes the fur or crust often seen lining tea- 
kettles and boilers. 

Freezing renders water much purer, by expelling a large 
proportion of its saline contents. Carbonate and sulphate 
of lime may be thus got rid of. But, like 1 boiling and dis- 
tillation, freezing expels the air and thus renders the water 
insipid. In all these cases the water regains its palata- 
bility on standing. 

421. Purification by Chemical Means. — The addition of 
two or three grains of alum to the quart cleanses muddy or 
turbid water, but often renders it harder than before. 
When alum is added, the water should not be used under 
twenty-four hours. Permanganate of potash destroys or- 
ganic matter and ammoniacal compounds by rapid oxidation, 
and may be used with advantage for this purpose. 

422. Filtration. — This is the most effective and prac- 
ticable method of purification, and is within the reach of 
every one. Many substances will answer as niters, such 
as crushed charcoal, sand, or porous sandstone, flannel, 
wool, sponges, or any other porous media. Of all these, 
charcoal is the best. It will remove eighty-eight per cent, 
of organic matter, and twenty-eight per cent, of minera] 
matters. If the water is moderately good, one pound of 
charcoal will purify six hundred pounds, or sixty gallons. 
Animal charcoal is better than vegetable, though both 
lose their purifying power sooner or later. It is quickly 



THE ALIMENTARY PRINCIPLES OF FOOD. 3S3 

restored, however, by exposure to air and slight heat. 
Filters of charcoal should be made of considerable thick- 
ness, and the coal finely crushed and well pressed to- 
gether. The effect of the charcoal is supposed to be 
chiefly chemical, as it brings the large quantity of oxygen 
which it holds into the closest contact with any oxidizable 
matters in the water. 

Sand is much used, and answers well for a time, but 
requires to be often renewed. 



CHAPTER XVII. 

FOOD AND HEALTH. 

Section L — The Alimentary Principles of Food. 

423, The Four Groups.— It was stated in Chapter VI, 
Section I., that all substances used as foods may be classed 
under four heads, either as Proteids, Fats, Amyloids, or 
Minerals. It is desirable to recapitulate and somewhat 
extend the observations there made. 

424. The Proteids. — This group of alimentary principles 
includes Gluten, Fibrin, Albumen, Syntonin, Casein, and 
Gelatin, which are characterized by the presence in their 
composition of a large amount of nitrogen. 

Gluti a is the adhesive principle of grain, and is a gray- 
ish, tough, elastic substance, left when the starch is thor- 
oughly washed away from flour. From its resemblance to 
the fibrous part of meat, it is known as vegetable fibrin. 
Animal fibrin exists dissolved in the blood, and solidifies 
into a fine net-work as the blood coagulates. It constitutes 
the bulk of lean meat Casein is the curdy principle of 

milk, which is Beparated by coagulation, and forms the 

chief ingredienl of cheese, It exists in large quantity 

(twenty to twenty-eight per cent.) in beans and peas, and 



384 ELEMENTARY HYGIENE. 

is known as vegetable casein. Albumen is a transparent, 
glairy, coagulable fluid, familiar to all as white of egg. It 
is a large constituent of animal fluid and tissues, and oc- 
curs in the seeds and juices of plants. Syntonin is the 
chief constituent of muscle or flesh. It closely resembles 
albumen in composition, but, unKke it, is not a product of 
the vegetable kingdom. Gelatin is an animal product, 
chiefly obtained from bones and tendons. It is not found 
in the vegetable kingdom, and is used for food, principally 
in the form of jellies and soups. 

All the foregoing substances, except gelatin, have a re- 
markable similarity of composition. They present varieties 
of aspect and physical properties, and differ in consistency, 
solubility, and behavior with heat : but they serve a com- 
mon purpose in the animal economy — that of furnishing 
material for the formation of the tissues — and on this ac- 
count have a high nutritive value, and are to a great ex- 
tent mutually replaceable. 

425. The Fats. — These cccur in both plants and animals, 
and, whatever their source, have a great similarity of com- 
position. Like the proteids, they differ in physical prop- 
erties, but are capable of replacing each other as articles 
of diet. They are essential to the formation of both mus- 
cular and nervous tissue, and, from their large amount of 
hydrogen and carbon, are the most energetic supporters of 
the heat-producing function. 

426. The Amyloids. — This group comprises the starches, 
sugars, and gums — principally vegetable products, which 
in one form or another constitute a large proportion of our 
ordinary food. Starch is abundant in grain, peas, beans, 
and potatoes. The different preparations known as sago, 
tapioca, arrow-root, and the like, consist almost entirely of 
starch extracted from different species of plants. Starch 
is capable of conversion into sugar, and is thus changed by 
the juices of the alimentary canal. Sugar is produced by 
both plants and animals, but our supply comes chiefly from 



THE ALIMENTARY PRINCIPLES OF FOOD. 585 

the vegetable kingdom, where it occurs m great abundance 
in Bap, fruit, ami seeds. By the agency of heat, starch 
may be converted into ffum^ known as dextrine. Gums 
are vegetable products widely distributed, but not in great 

abundance. Their composition is similar to that of starch 
and sugar, and their dietetical function is supposed to be 
the same. 

427. Their Offices. — It lias until lately been supposed 
that as the nitrogenous and non-nitrogenous substances are 
clearly separated by chemical compositions, they are also 
sharply divided in their physiological effects. The first 
were supposed to nourish the tissues, the decomposition 
of which was believed to be the sole source of animal 
power, while the fatty and amyloid group served only to 
maintain animal heat by their oxidation. But, while it is 
believed that the bodily tissues can only be reproduced 
from the nitrogenous elements, it is admitted that the de- 
composition of these tissues must be a source of heat; and 

•nt researches have established that the combustion of 
the hydro-carbons is a source of power, part of the heat 
produced being converted into mechanical force. 

428. Mineral Aliments. — The inorganic or mineral con- 
stituents of food consist of water and various saline sul>- 
Btances. Common salt occurs in all forms of food, but in 
larger proportion in animal than in vegetable tissues. An 
instinctive craving impels animals to sock for a larger sup- 
ply of it than is furnished in their food. Chloride of potas- 
sium, phosphate of lime, and alkaline carbonates, arc indis- 
pensable to digestion, and are furnished in combination 
with tin' various aliments 

429. Necessity for a Mixed Diet. — The usual forms of 
food an- combinations of these alimentary principles. Milk, 
for example, is a highly-complex animal product, contain- 
ing water, casein, butter, sugar, and. various mineral salts 
— representatives of each of the four classes <•!' alimentary 
principles. By it- excess of salts and nitrogenous mattei* 



386 ELEMENTARY HYGIENE. 

it is suited to the wants of the infant, or the period of 
rapid growth, but it is not a complete or properly-balanced 
diet for the adult. In the majority of cases, no single ar- 
ticle of food is thus perfect in composition, there being 
usually one or more of the essential elements of a suitable 
diet wanting. This is the case with the various meats, all 
of which abound in nitrogenous and fatty substances, but 
are deficient in the amyloid elements. On the other hand, 
most vegetables are rich in starch and sugar, but deficient 
in nitrogenous matters. Bread is nitrogenous, amylaceous, 
and inorganic, but lacks fat ; while Indian-corn contains 
less of the nitrogenous element, but a large amount of 
starch, and eight or ten per cent, of fat. As no one article 
of food, therefore, contains these four classes of materials in 
the proportions requisite to a perfect diet, we are obliged 
to mix our various food-stuffs. Confinement to a single 
alimentary principle, or to any one class of them alone, is 
sure to be followed by disease. It has been shown, bv re- 
peated experiments, that dogs confined to the exclusive 
use of either starch, fat, or albumen, soon die of starvation. 
Like experiments begun upon men were productive of a 
corresponding disturbance, and doubtless, if carried out, 
would have ended in the same way. 

The proteids are first in importance, as much the larger 
part of the mass of the body is derived from them, and, 
when given alone, they sustain its powers longer than any 
other class of aliments. Hence, it is easy to see why ex- 
haustion follows so much more quickly when they are 
withheld, than when other kinds of food are unsupplied. 
But the amyloids, fats, and minerals, are also requisite, 
and the body feels the want of them sooner or later, even 
though the proteids are furnished in abundance. 

Section II. — Animal Foods. 

Foods may be conveniently divided into three classes : 
animal food, vegetable food, and auxiliary food. Sub- 



ANIMAL TOO - 

incefl derived from animals. Bach as milk, eggs, and 
meats, are exampl - si lass. 

43G. Milk. — As this Liquid contains all the elements 
necessary tor complete nutrition, it has been regarded 
the type of compos a, but, as jusl remarked, it is 

mpletely adapted to a certain stage of animal life. 
A hundred parts - atain of casein, 4.48 ; 

butter, 3.13; of milk-sugar, 4.4, ~: salts, 1 of water. 

12. This, however, is only an average statement, a- no 
two cows give milk exactly alike in composition, while the 
milk of the same cow varies with the food. The milk of 

is and ewes is richer in solids than that of the COW. 
Human milk is poorer in casein, and contains a larger pro- 
portion of sugar than cow's milk ; this is the reason why 
the latter is diluted and sugared when employed a.> food 
for infants. 

In cities, milk is often adulterated with water. If much 

wal een added, it may 1 i >y applying the 

t.'<t. The specific gravity of unadulterated 

milk ra _ s fi >m 1.026 to 1.033; the a - about 

Two parts water to eight parts milk will redu 
its specific gravity to 1.024 : four parts water to six parts 
milk, to 1.018 ( ! milk should be of a full white color, 
per:" paque, without f and free from any pe- 

culiar taste or smell. It should give a neutral reaction, 
and have a specific gravity of at least 1.1 

431. Butter and Cheese — These furnish the nutritive 
constituents of milk in a concentrated form. Butter IS 

►itually associated with substances which are deficient 

in far, and i> hell to promote their diL r <*-til>ilitv. All 
butter contains casein, which is derived from the milk 

r with the cream, hut tb< in- the 

liable 1* idity is *ing to 

the oil product 1 by decomposition of tin- casein. 
it for fo b is indi_- 

tib! . kn two to produoe dyspepsia and diar- 



388 ELEMENTARY HYGIENE. 

rhoea. Cheese is rich in nitrogenous material, and when 
fresh is regarded as excellent food. It is very liable, how- 
ever, to undergo chemical change, and when this is once 
set up it becomes irritating and indigestible, especially if 
eaten in considerable quantity. The peculiar flavor of old 
cheese arises from this commencing decomposition, and it 
often disturbs weak stomachs. In this condition, however, 
it is said to promote the digestion of other substances, and 
for this reason is sometimes taken in small quantities as a 
condiment. 

432. Eggs. — These are both nitrogenous and fatty, and, 
when properly cooked, are easily digested and highly nutri- 
tious. They contain no starch or sugar, and should there- 
fore be eaten in ccnnection with such articles as supply 
these aliments. Eggs are most w 7 holesome when boiled 
sufficiently to coagulate the white without hardening the 
yolk. Hard boiled or fried eggs digest with difficulty. And 
eggs that have been kept long, though not spoiled, are less 
digestible than fresh ones, 

433. Meats. — Whatever their source, these are esssen- 
tially the same in constitution, that is, they all contain a 
large amount of nitrogenous matter, in union with much fat 
and various important salts. Their advantage as a diet is, 
that they contain a large amount of nutriment in a highly- 
concentrated form, are easily digested when properly cooked, 
and admit of ready assimilation. 

Fresh meat varies in quality with different animals, and 
with the age, sex, and condition of the individual from 
which it was obtained, as well as with the character of the 
food upon which it was fattened. Stall-fed cattle make 
the finest beef, and corn-fed swine the best pork. The 
nicest mutton is obtained from sheep fattened on fresh, 
succulent pasturage r In all cases the animal should be 
free from disease, and of medium fatness, to make its flesh 
a healthly and economical food. The muscle should be of 
a firm yet not sodden consistence, of a pale-reddish color, 



ANIMAL FOODS. 389 

somewhat lighter toward the centre than at the surface, 
and show no disposition to tear across its fibres. The fat 
should be white, or but slightly tinged with yellow, and 
also firm to the touch. The pale, moist muscle marks the 
young animal ; the dark colored, the old one. The meat 
should be free from any disagreeable odor, and the mus- 
cles, when cut across, should present a uniform solidity. 
Any marbling, or points where the knife passes more 
easily than at others, indicates commencing decomposition; 
As a rule, the flesh of young animals is tenderer and more 
sily digested than that of old ones; veal, however, is an 
exception, so far as digestibility is concerned. The flesh 
of voumy animals contains more water than that of old 
ones, consequently it is more juicy, but, bulk for bulk, less 
nutritious. 

434. Salt Meat. — Beef and pork an 1 commonly pre- 
ved for future use by salting, and in this condition are 

largely employed as food. Salting, however, reduces the 
nutritive value of meat, detracts from its flavor, and ren- 
ders its digestion more difficult. It does this by extract- 
ing a portion of the juices, which remain dissolved in 
the brine, thus leaving the fibres of the meat harder and 
consequently less easily acted upon by the fluids of the 
stomach. 

435. Poultry and Game.— Meat of this kind is more 
jily digested than that just considered, but is regarded 

as le>s nutritious. It is not so juicy as butcher's meat, 
and as a rule contains less fat. Brothfl made from it have 
a delicate flavor, and contain considerable nutriment, hence 

they make an excellent food for convalescents. 

436. Fish. — The flesh of fish i< v( ry similar in composi- 
tion to that of other animal-. Il IS SOmewhal poorer in 
nitrogenous matter, but richer in important salts, and con- 
tains a larger proportion ' f water than butcher's meat. 

It is generally of easy digestion, but it should not be 
>\ exclusively, nor for along period together, as it i^ 



390 ELEMENTARY HYGIENE. 

liable to produce a scorbutic state of the system. The 
flesh of fish undergoes rapid decomposition, and is then 
highly injurious. It should be eaten only when it is per- 
fectly fresh. Salt fish, like salt beef or pork, is much 
inferior to fresh, and extremely indigestible. 

437. Crabs and Lobsters. — The flesh of these animals 
resembles that of fish, but it is less easily digested. It 
is peculiarly prone to decomposition, and when eaten in 
this state often produces sickness which sometimes proves 
fatal. 

438. Clams and Oysters. — Clams, either raw or cooked, 
are difficult to digest. Oysters are much less so. They 
are most easily digested w r hen raw, and, if cooked, should 
be either stewed or roasted. 

Section III. — Vegetable Food. 

439. Wheat. — Of vegetable food-stuifs, the most im- 
portant and widely-used are the cereal grains. Among 
these wheat ranks first, both in point of nutritive value and 
in the ease with which it is digested. With the exception 
of milk, it approaches more nearly the standard of a perfect 
food, and will sustain the powers of the body for a longer 
period, than any other single article of diet. It contains 
from ten to fifteen per cent, of gluten ; from sixty to seventy 
per cent, of starchy matter, and a small proportion of fat, 
besides certain important alkaline and earthy phosphates. 
Its proportion of water is very low, averaging about twelve 
per cent. ; bulk for bulk, therefore, it is richer in solids than 
any other food. The starchy elements of the seed exist most 
abundantly in and about its centre, while its glutinous, fatty, 
and mineral constituents, are found in greatest quantity 
towards the surface. The coat immediately beneath the 
husk is especially rich in gluten, and therefore highly valu- 
able as food. In the process of grinding, this is often lost 
by passing into the bran, the result being a whiter but 
\nuch less nutritious flour. The soft wheats yield the 



VEGETABLE FOOD. 391 

whitest flours, as they contain more starch and less gluten 
than the hard or flinty varieties. Good wheat should yield 
at least eighty per cent, of Hour. 

The quality oi wheaten flour may be best determined 
by the practical test of baking. Still, something may he 
told by it> appearance. It should contain very little bran, 
and its starch should be white, or with the very slightest 
tinge of yellow. The flour ought not to ho lumpy, or, if so, 
the Lumps should readily give way under the slightesl press- 
ure. Grittiness indicates that the starch-grains are chang- 
ing, and such flour will give an acid bread. When com- 
pressed in the hand, good flour will adhere in a lump, and 
retain the imprints of the fingers longer than that of inferior 
grade. If cast against the wall, a portion should stick 
firmly to its surface. The dough made with good flour is 
ductile and elastic, and may be drawn out into long strips, 
or rolled into thin sheets without breaking. 

Flour becomes whiter with age, but it is at the expense 
of flavor, sweetness, and nutritive value. The greater the 
proportion of gluten, the sooner will this deterioration 
take place. Flour is sometimes contaminated by the pres- 
ence of fungi or insects, and they always indicate inferior 
quality. It is also occasionally adulterated with the flour 
of other grains, which can only be detected by the micro- 
scope. 

440. Rye. — This comes next to wheat in nutritive value, 
though it furnishes less flour to the bushel, and that of a 
decidedly darker eolor. Its gluten appears to contain more 

•in .and less vegetable fibrin than that of wheat, conse- 
quently it is less tenacious. Owing to this quality, bread 

made from rye-flour doe- not rise well, and is liable In 

become heavy on cooling. Rye-bread soon becomes acid, 
and with many i- not easily digested. 

441. Buckwheat. — Tin- is poor in nitrogenous and fatty 
constituents, but rich in starch. Bread made from buck- 
wheat-flour does not rise well, owing to its deficiency in 



392 ELEMENTARY HYGIENE. 

gluten. It is, therefore, chiefly consumed in making griddle- 
cakes, which, while warm, are light and palatable, but not 
well received by weak stomachs. 

442. Indian-corn contains a much larger proportion of 
fat than any other grain in common use. It is also rich in 
starch, but has far less nitrogenous matter (zein) than 
either wheat or rye. This principle is not of a glutinous, 
adhesive nature, and hence maize-flour, or meal, will not 
make a dough, or fermented bread. In the preparation of 
articles of food from Indian-meal, long cooking is necessary, 
when it makes both a palatable and highly-nutritious food, 
which is easily digested. 

443. Oatmeal is rich in gluten and fat, and also contains 
a fair proportion of starch and sugar. It does not make 
good bread, but is commonly cooked by stirring with boil- 
ing water until it has the consistence of hasty pudding. It 
should be thoroughly cooked, when it is palatable and 
highly nutritious. It is less digestible, however, than 
wheaten products. 

444. Rice. — As an article of diet, rice possesses the ad- 
vantage of an extremely digestible starch-grain. It has, 
however, but small proportions of nitrogenous matter, 
fat, and salts ; hence, in rice-eating nations, it is habitu- 
ally taken with such other food as will best supply these 
wants. 

445. Peas and beans are much alike in composition, and 
both rich in nitrogenous constituents, often containing as 
high as twenty-six per cent, of vegetable casein, or legumen. 
They also contain much sulphur and phosphorus, together 
with an average proportion of salts, and but a small quantity 
of water. They are, therefore, very nutritious, and rank first 
among concentrated, strength-imparting foods. But they 
are somewhat indigestible, and liable to produce flatus. 
When eaten, it should be in small quantity, and only by 
those of an active habit of body. 

446. Succulent Vegetables. — Of these, potatoes are the 



VEGETABLE FOOD. 393 

most valuable and most extensively used. They contain in 

100 parts- 
Water 74 

Proteida 1.5 

Fats 1 

Amyloids 23. t 

1 

They are thus seen to abound in amylaceous materials and 
salts, but contain a low proportion of nitrogenous matter, 
and very little fat. Owing to this deficiency, we habitually 
associate them with meat, when they form an easily digested 
and valuable food. 

Turnips, beets, carrots, parsnips, etc., contain more 
water than potatoes, and are not so easily digested. Their 
solid portions consist mainly of starch and sugar, with a 
small percentage of fat and salts. They each possess a pe- 
culiar volatile principle,- which adds much to their flavor, 
and causes them to be eaten more as a relish than as a 
strength-giving food. 

Onions and cabbage are more watery than the preced- 
ing, but their solid parts contain a very large proportion 
of nitrogenous matter. They are relished chiefly for their 
pungency, bul should be eaten only at intervals, as they are 
likely to cause flatus and indigestion. 

447. The Fruits. — These consist mostly of water and 
cellulose, with varying amounts of fruit-sugar, and small 
quantities of potash, soda, and lime, in combination with 
certain organic acids. Their juices contain a gelatinous 
substance termed pectine, which form- the basis of the va- 
rious jellies. Fruits are prized more for those qualiti 
which relate to their taste than for nourishing and strength- 
tug power. Nevertheless, they are valuable as bout 
of the alkaline and earthy carbonates, and useful when eaten 
in moderate quantity, as safeguards against constipation 

They are most wholesome when cooked, but in all cases the 



394 ELEMENTARY HYGIENE. 

skins, seeds, and cores, should be rejected, as indigestible, 
and prolific sources of irritation. 

Sectiox IV. — Auxiliary Foods. 

448, — Auxiliary foods comprise a class of substances 
very extensively employed to give relish to other dietarv 
compounds, to provoke the digestive organs, and for ner- 
vous stimulation, rather than for any nutritive properties 
of their own. Useful when taken with care, the}' are 
liable to prove most injurious when too freely indulged 
in. Under this head come the various condiments and 
beverages. 

449. The Condiments. — Vinegar is essentially a solution 
of acetic acid in water. Good vinegar ought to contain at 
least five per cent, of the acid. Commercial vinegar is often 
largely adulterated, and some samples which pass under 
the name are made of sulphuric acid and water, colored 
with burnt sugar, and without a trace of acetic acid in 
their composition. Vinegar in small quantities, by aug- 
menting the acidity of the stomach, may reenforce the 
gastric juice, and promote the digestion of the proteids. 

Black pepper consists of an active principle (piperin), 
a pungent essential oil, and an acrid resin. It is a power- 
ful stimulant of the digestive organs, increasing the flow 
of saliva and gastric juice in a marked degree. In the 
powdered state it is frequently adulterated with linseed- 
meal, starch, mustard, buckwheat-bran, etc. These may 
be detected by the microscope ; but it is safest to purchase 
the berries and grind them as wanted. 

Cayenne pepper resembles black pepper in properties, 
but is a much more powerful stimulant. Its habitual use, 
therefore, cannot be recommended, and, if taken at all, it 
should be only in the smallest quantity. 

The sharp, acrid smell and taste of mustard are due to 
the volatile oil it contains. Used in small quantities, it is 
a gentle stimulant ; in large doses, it acts as an emetic. 



AUXILIARY roODfi 395 

Like all articles of it- class, it is subject to sophistication. 
Among the substances added, the most common are tur- 
meric and some form «>t' Btarcb. Sulpha 4 e of lime and 
chalk are als<> sometimes used as adulterants. 

450. Beverages. — Tka. — Thia consists of the leaves of 
th i teashrub, grown and prepared chiefly in China. Many 
varieties are known in commerce, the differences between 
which are due probably to different modes of culture and 
preparation. 

The substances for which tea is most prised as a bever- 
are— -first, a peculiar volatile oil, which gives the tea 
its agreeable flavor; second, a vegetable alkali, rich in 
nitrogen, and known as ifu in — the active principle ^( tea; 
and third, tannic acid, which gives the tea its astringent 
quality. Of the first, tea contains less than one per cent ; 
of the second, from one and a half to six per cent. ; and of 
the tannic acid, which i- in combination with the thein, from 
fourteen to sixteen per cent. It contains, besides, about 
twenty per cent, of gluten, and is also rich in Baits, but 
these last ingredients tire not usually obtained in the bev- 
erai: 

In making tea. it is desirable to obtain from the leaves 
sible amount of matter, without destroying 

flavor. If the tea is boiled, the volatile oil is driven 
off with the steam — and yet a boiling temperature is re- 
quired to dissolve the compound of thein and tannic acid, 
the most important constituent of the leaf. To preserve 
and obtain the other i< the principal object, and 
• attained by pouring boiling water upon the 
leaves in close vessels, and allowing them to steep for a 
time, with the temperature slightly below the boiling- 
point 

gentle stimulant to the d< 
t -m. without pro lu dng tent perceptible depression. 

It also quickens tip- pulse somewhat, and inc the 

amount of pulmonary carbonic acid exhaled. It prodi* 



396 ELEMENTARY HYGIENE. 

an astringent effect upon the bowels, but not to any harm- 
ful extent. It hastens digestion and is invigorating, but 
should not be taken in excess, as it is apt to induce wake* 
fulness and an irritable state of the system. Green tea 
is more injurious than black, often giving rise to nervous 
tremors. 

Tea of all sorts is liable to the grossest adulteration, 
green teas being worse in this respect than the black 
varieties. The Chinese heighten the color of the leaves 
or face them, as it is termed, by the addition of Prussian 
blue, indigo, turmeric, gypsum, and China clay. A bright- 
green color is to be looked upon with suspicion, as the 
pure article always presents a dull, faded green appear- 
ance. The leaves of other plants are often mixed with 
tea. Sometimes, also, exhausted tea-leaves or grounds are 
bought up, astringency imparted to them by the addition 
of catechu, and, colored with black lead, or logwood, they 
are sold again as genuine tea. Another fraud of great 
prevalence consists of mixing inferior qualities of tea with 
better sorts, and cheating the purchaser by selling the 
compound at the price of the best article. 

In selecting tea, it should be but little broken up, 01 
mixed with dirt, and the leaves should vary somewhat in 
size and color. The best teas contain portions of the 
stalk and flower. Old teas do not possess so rich a flavor 
as fresh, owing to the loss of a portion of their volatile oil. 

451. Coffee. — Coffee, like tea, contains a volatile oil, a 
vegetable alkali (caffeiri), and tannic acid. It also contains 
from twelve to fifteen per cent, of amylaceous material, in the 
shape of sugar and gum, and nearly the same quantity of 
nitrogenous matter, in various forms, besides being rich in 
salts. But very small quantities of these latter substances 
find their way into the beverage. 

The agreeable flavor of coffee is due to its volatile oil, 
which is present in very minute proportions, and requires 
the action of heat to develop it. This is done by the pro 



AUXILIARY FOODS. 397 

58 of torrefying. The caffein is almost identical in com- 
position with the thein of tea, and, like it, is the active 1 
principle of the beverage. It is present in small quantity, 
rarely reaching one percent The quantity o( tannic acid 
is usually less than six per rent., consequently coffee is n )\ 
so astringent as tea. 

The action of coffee upon the system is similar to that 
of tea. It is a stimulant, and promotes the digestion and 
assimilation of food. It both enlivens the mind and invigo- 
rates the body, relieving the depression of fatigue, and in 
thie way undoubtedly tends to diminish the liability to 
di>ease. 

There is a peculiar physiological effect exerted by coffee 
and +ea, and probably also by alcoholic beverages when 
taken in small amount — a retardation cf destructive meta- 
morphosis. The renal products of muscular waste are 
found to be diminished after their use; while experience 
has shown that they may- replace, in diet, a certain amount 
of ordinary food. De Gasparin, in his observations upon 
the regimen of the Belgian miners, found that "the addi- 
tion of a quantity of coffee to the daily rations enabled 
diem to perform their arduous labors on a diet which was 
even below that found necessary in prisons and elsewhere, 
where the article was not employed." The comparative 
effects of coffee, tea, and alcohol, in enabling men to endure 
eold and hardship, are thus stated by \)\\ Hayes, in describ- 
ing the experiences of arctic exploration: "Dr. Kane's 
parties, after repeated trial, took most kindly to coffee in 
the morning, and tea in the evening. The coffee Beemed 
to last throughout the day, and the men seemed to grow 
hungry less rapi Hy after taking it than after drinking tea, 
while tea soothed them after a day's hard labor, and the 
better enabled them to sleep. They both operated upon 

fatigued and overtaxed men like a charm, and their supo 

riority over alcoholic stimulants was very marked/' 

In the process of roasting, the coffee should be first 



398 ELEMENTARY HYGIENE. 

carefully dried in an open pan, over a gentle fire, until it 
becomes yellow. It should then be scorched, in a covered 
vessel to prevent the escape of aroma, taking care, by 
proper agitation, to prevent any portion from being burnt, 
as a few charred grains communicate a bad odor to the rest 
The operation should be continued until the coffee acquires 
a deep cinnamon or chestnut color, and an oily appearance, 
or until the peculiar fragrance of roasted coffee is sum 
ciently strong. Unroasted coffee may be kept for any 
length of time, and grows better with age. After roasting, 
it is constantly losing flavor ; hence, it is well to roast but 
a small quantity at once, and this ought to be kept in close 
vessels, and ground as it is wanted for use. This course 
necessitates the purchase of the berry and home prepara- 
tion, but the additional trouble is more than compensated 
by the superior beverage thus obtained. The finer it is 
ground, the more readily, of course, will it yield its solu- 
ble constituents. 

Ground coffee is very extensively adulterated ; another 
inducement for purchasing the whole berries. Various 
substances are employed as adulterants, such as roasted 
peas, beans, corn, turnips, carrots, potatoes, etc. But the 
substance most commonly used is chiccory, which has a 
large white parsnip-like root, abounding in a bitter juice. 
A little of this, when roasted, gives as dark a color and as 
bitter a taste to water as four times the quantity of coffee, 
and, as it only costs about one-third as much, the tempta- 
tion is very strong to mix it with ground coffee. So great 
is the demand for chiccory for this purpose, that it is itself 
adulterated with roasted barley and wheat grains, acorns, 
mangel-wurzel, sawdust, peas, and beans. Venetian red is 
sometimes added to give it a coffee-color, and even this is 
cheapened by the addition of brick-dust. The microscope 
detects many of these foreign substances, while some can 
be identified only by chemical means. 

In the preparation of the beverage, we are met by the 



CULINARY PREPARATION OF FOODS. 399 

difficulty thai was encountered in the case of tea; that 
is, a high heat will drive off the aroma, while yet it is re- 
quisite to the extraction of the active principle — caffein. 
To obviate this, take two portions of coffee, boil the first 
for five minutes in the required amount of water; then, 
after settling a moment, decani the water upon the sec- 
ond portion, and allow it to steep for a few moments 
without additional heat. After it has settled, pour oil* the 
liquor for use, and retain the grounds for the next day's 
boiling. A lYosh portion furnishes the aroma, and ran 
in its turn be subjected to the boiling process. 

452. Cccoa and Chocolate.— These are prepared from 
OQrbeans^ which are derived from a fruit resembling a 

short, thick cucumber, grown upon the small coeoa-tree of 
the West Indie-, Mexico, and South America. The bean 
is brittle, of a dark-brown color internally, and has a slightly 
astringent but decidedly bitter taste. In preparing it for 
use, it is roasted in the same way as coffee, until the aroma 
is fully developed. The bean is now more brittle, lighter 
in color, and less a>tringent and bitter than before. The 
beans contain about fifty per cent, of fatty matter, called 
butter of cocoa, and from twenty to twenty-five per cent, of 

albuminous and starchy material. They also contain a pecu- 
liar nitrogenous substance called theobromine similar in na- 
ture and properties to thein and caffein. The beans crushed 
to a paste between hot rollers, and mixed with starch, sugar, 
etc.. form common cocoa* Chocolate is made by grinding 
the recently-shelled beans to paste, mixing this with sugar, 

and flavoring it with vanilla, cinnamon, and the like. 

When used n- a beverage, the chocolate or cocoa i> scraped 

into powder, mixed with water and milk, and brought to a 

boiling heat. As thus prepared, chocolate is refreshing to 
the spirits, and highly nutril ion-. 

Section V. — Culinary Pn paration of Fowls. 

453. Cooking has a twofold object— r/'V< fco -often the 



400 ELEMENTARY HYGIENE. 

food, and thus facilitate its solution in the digestive juices; 
and second, to develop its flavor, and thus render it more 
agreeable to the palate. When the operation is properly 
performed, both these purposes may be attained, and yet 
by improper management both may be defeated. For ex- 
ample, in cooking meats, it is desirable to retain their 
flavor, preserve their juices, and soften their texture, and, 
with the requisite care, all this may be accomplished ; yet 
how often does careless or improper management give us 
a hard, dry, tasteless mass, as indigestible as it is unpala- 
table ! Over-cooking should be specially avoided, as it re- 
sults in waste and loss of sapidity, without in any respect 
improving the character of the food. 

454. Cooking of Meats, — Boiling. — Meats lose from 
twenty-five to thirty-five per cent, of their weight by this pro- 
cess. If it is desired to retain their juices and flavor, the 
pieces should be cut large, and, when first put in, the water 
should be boiling. This coagulates the albumen near the 
surface of the piece, and thus prevents further escape. After 
boiling three or five minutes, the heat should be lowered to 
about 1 60°, and maintained at that point until the completion 
of the process. If the temperature is kept above 170°, the 
muscular tissue shrinks, and becomes hard and indigestible. 
In making broth, the object is to extract the juices ; hence 
the meat should be cut into small pieces and placed in cold 
water. After standing a little time, it may be slowly 
heated to about 150° ; never much above this. Coagulation 
of the albumen is thus prevented, and the contained juices 
extracted. A nutritious beef-broth, or beef -tea, may be 
made without heat, by adding to a pint of cold water half 
a pound of finely-cut, fresh, lean beef and four or hv2 
drops of hydrochloric acid. Slight heat and a few drops 
more acid considerably increase the amount of extract. 

Roasting is one of the best methods of cooking meat. 
It not only develops the flavor, but preserves the juices, 
and leaves the meat in a condition to be easily digested. 



CULINARY PREPARATION OF FOODS. 401 

The loss is about twenty-five per cent., and is chiefly water. 
The process should be commenced with an intense heat, 
in order to coagulate the albumen of the surface and form 
a thin superficial crust. Afterwards it should be done very 

slowly, so as to avoid hardening the inner portions. 

S wing is analogous to roasting, only the meat is cut 
up, and continually moistened with its own juices. Like 
boiling and roasting, it should be done at a low heat. 
Tough meat is best cooked in this manner. Baking re- 
quires to be conducted with great care, or there is danger 
of drying up the meat. Constant basting prevents this to 
some extent, but the method is inferior to roasting. Fry- 
ing is the worst possible way in which meat can be cooked. 
The oil or fat requiring a high temperature to bring it to 
the boiling-point, the meat is thus rendered extremely 
hard and the fat not unfrequently burned. Broiling is to 
be preferred to frying. It has much the same effect as 
roasting, and, like that process, should not be carried too 
far — a high heat at first, sufficient to incrust the outside, 
and then a low temperature to complete the work. 

455. Cooking of Vegetables.— Th esc are usually boiled, 
and are best cooked by this means. Care should be taken 
not to overdo them. Thorough softening is sufficient, as, 
when the process is carried beyond this, their structure 
is rapidly broken down, and a large proportion of their 
salts and juices lost in the water. The quality of the 
water employed exercises an important influence. Soft 
water exerts a much more powerful extractive action than 
hard, hence food boiled in it is oftentimes rendered insipid 
by the loss of it>> salts and juice-. When it LS desirable 

to obtain these in a liquid form, as in making soups, broths, 
or infusions, Bofl water i- to be preferred. In those cases 
where it i- not the object t.» dissolve em th" contents of a 
structure, but rather to preserve it fnm and entire, hard 
water is the best. To prevent the over-dissolving action 
a .ft water, salt is often added, and proves quite effectual. 

• 



402 ELEMENTARY HYGIENE. 

Section VI. — Injurious Effects of Bad Diet. 

456. Effects of Excess in Diet.— The influence of food 
upon health is immediate and powerful, and is manifested 
in various ways. Imperfect diet is chiefly injurious by its 
excess, by its deficiency, by the wrong proportions of its 
elements, and by the unwholesome condition of the articles 
consumed. 

The quantity of food that it is proper to take, varies, 
of course, with different circumstances : those thinly clad 
and exposed to cold require more than the well protected ; 
those in active exercise more than the sedentary or per- 
sons of inactive habits ; while the growing need, propor- 
tionally to their size, more than adults. But whatever the 
circumstances, if the quantity of food taken exceed the 
demands of the system, evil consequences are certain to 
follow. The immediate results of over-eating are lethargy, 
heaviness, and tendency to sleep. Overtaxing the digestive 
organs soon deranges their functions, and is a common and 
efficient cause of dyspepsia. If the food is not absorbed 
from the digestive apparatus into the system, it rapidly 
undergoes chemical decomposition in the alimentary canal, 
and often putrefies. Large quantities of gas are thus gen- 
erated, w 7 hich give rise to flatulence and colicky pain. 
Dyspepsia, constipation, and intestinal irritation, causing 
diarrhoea, are produced. If digestion be strong, and its 
products are absorbed, an excess of nutriment is thrown 
into the blood, and the circulation overloaded. If food is not 
expended in force> the natural alternative is its accumula- 
tion in the system, producing plethora and abnormal in- 
crease of tissue. This is accompanied by congestion of 
important organs, mal-assimilation of nutritive material, 
and increased proneness to derangement and diseased ac- 
tion. The excretory processes are likewise certain to be 
disturbed, which often leads to the retention of waste 
products, with perversion and poisoning of the blood, 
and a train of evil consequences. 



INJURIOUS EFFECTS OF HAD DIET. 403 

457, Effects of Deficient Diet. — As food is the source 
alike of the material organism and of the power it exerts, 
if a due supply of it is withheld, there is defective nutri- 
tion, which reduces the structures and impairs thestrength. 
Habitual insufficiency of food lowers the vital powers and 
depresses the functions. There is loss of mental vigor 
and muscular energy, and a tendency to digestive disturb- 
ance, anaemia, and the development of those maladies 
which result from debility and undervitalized conditions. 
The resistance of the system to the numerous causes of 
disease is diminished : typhus and typhoid fevers are pe- 
culiar diseases of the poorly fed. In childhood, lack of 
sufficient food is often the cause of stunted growth and 
chronic disease, and in later life the parent of depraved 
appetites and moral perversities. 

Of the effects of stinted food upon mind and character, 
Dr. Moleshott observes: "There is another instinct by 
which the vigor of mind is vanquished in a more melan- 
choly way. Hunger desolates head and heart. Though 
the craving for nutriment may be lessened to a surprising 
degree during mental exertion, there exists nothing more 
hostile to the cheerfulness of an active, thoughtful mind, 
than the deprivation of liquid and solid food. To the 
Btarving man, every pressure becomes an intolerable bur- 
den ; for this reason, hunger has effected more revolutions 
than the ambition of disaffected subjects. It is not, then, 
the dictate of cupidity or the claim of idleness which 
prompts the belief in a natural human right to work and 

458. Amount of Food daily required.— Although this is 
variable in different circumstances, yet definite standards 
have been reached when dealing with large bodies of men 

in given cases. It has been shown that generally, in the 

the adult male, from ten to twelve ounces of carbon 
and from four to five ounces of nitTOgenized matter (esti- 
mated dry) are daily discharged from the organism, and 



404 ELEMENTARY HYGIENE. 

that, to replace this, there is required a daily consumption 
of from two to three pounds of solid food. Dr. Dalton 
says : " From experiments performed while living on an 
exclusive diet of bread, fish, meat, and butter, with coffee 
and water for drink, we have found that the entire quantity 
of food required during twenty-four hours, by a man in 
fall health, and taking free exercise in the open air, is as 
follows : 

Meat . . . .16 ounces, or 1.00 lbs. avoirdupois. 

Bread . . 19 u " 1.19 " 

Butter, or fat . . . 3£ " " 0.22 " 

Water ... 52 fluid-oz. " 3.38 " 

That is to say, rather less than two and a half pounds of 
solid food, and rather over three pints of liquid food." 

" It is undoubtedly true that the daily ration has fre- 
quently been diminished considerably below the physiolo- 
gical standard in charitable institutions, prisons, etc. ; but. 
when there is complete inactivity of body and mind, this 
produces no other effect than that of slightly diminishing 
the weight and strength. The system then becomes re- 
duced without any actual disease, and there is simply a 
diminished capacity for labor. But in the alimentation oi 
large bodies of men subjected to exposure, and frequently 
called upon to perform great labor, the question of food is 
of vital importance, and the men collectively are like a 
powerful machine, in which a certain quantity of material 
must be furnished in order to produce the required amount 
of force. This important physiological fact is most strik* 
ingly exemplified in armies ; and the history of the world 
presents few examples of warlike operations in which the 
efficiency of the men has not been impaired by insufficient 
food. 

" The United States army-ration is the most generous in 
the world ; and the result has been that, in the recent civil 
war, scurvy and other diseases which are usually so rife in 



INJURIOUS EFFECTS OF BAD DIKT. 405 

armies subject to the exposure and fatigue incident to 
grand military operations, have been comparatively rare. 
In some of the long and arduous campaigns of the war, 
the marches made by large bodies of troops, and the labor 
performed, showed an amount of endurance heretofore 
unknown in military history. The excellent physical 
condition of the men was further evidenced by the remark- 
able percentage of recoveries after serious wounds and 
surgical operations, and the slight prevalence of the 
ordinary diseases, except those of malarial origin." — (\)v. 
Flint.)* 

The following is the army-ration of the United States 
soldier : 

Bread <>r flour ...... 22 ounces. 

ah or Bait beef (or pork or bacon, 12 <>/..) . 20 

P< t;a«)f> (three time- per week) ... 16 

Rice 1.0 

c See or tea, 0.24 oa) .... 1.6 " 

3 Igar ........ 2.4 

Beans < 1.64 gill. 

Vinegar .... ... 0.32 u 

Salt 0.16 u 

459. Effects of a badly -constituted Diet. — There may be 
sufficient bulkiness in the food taken, hut such a mispropor- 
tion among it- elements as to perveH the functions and 
-■ivr rise to various maladies. The several elements of 
food-stuffs are not replaceable. Deficiency of the proteids 
results in muscular debility and prostration; while, it' too 

,t a quantity be taken, they charge the system with 
imperfectly-assimilated compounds and wr tngly-changed 
products of decomposition, which produce a gouty state of 
the constitution. Deficiency of the fats induce defective 
nutrition and leanness; while exoe - of them not only 
tend- to produce obesity, hut. if more be taken than can be 

ed or consumed, the burden of disposing of the i \ «ss 
fall- upon the liver, which may it-elf become diseased from 



406 ELEMENTARY HYGIENE. 

1 over-action, or its secretions be thrown into the blood, giv- 
ing rise to a bilious condition of the system. If the saline 
elements are withheld, softening, or deformity of the bones, 
or rickets, is the legitimate consequence. If the supply of 
fresh vegetable food is cut off for a lengthened period, a 
scorbutic condition of body is produced. Hence, for the 
preservation of health, mixed food and a various well-bal- 
anced diet are indispensable. 

In the case of infants and children, where food sub- 
serves the double purpose of maintaining activity and 
growth, there must be extra provision in the diet for the 
development of muscular and bony tissues. Milk, though 
a liquid, by its abundance of salts and casein, is adapted to 
this end. But too frequently, after weaning, the food of 
children is given with no reference to this important condi- 
tion. Sago, tapioca, arrow-root, and jellies, which rank 
lowest in nutritive value, with perhaps other substances 
less objectionable, but still inadequately nourishing, are 
frequently made use of, to the serious injury of the growing 
constitution. 

460. Effects of a Deficiency of Fat. — It is believed that 
a lack of oleaginous elements in diet predisposes to con- 
sumption. The immediate cause of this disease, as has 
been already observed, is an abortive or perverted nu- 
trition, tubercle being produced instead of healthy tis- 
sue. The seeds of consumption are most generally sown 
in the system in youth, when there is a double demand 
upon nutrition, for current waste and steady growth. 
There is, however, sufficient proteid matter present to 
nourish the structures ; some other condition must, there- 
fore, be wanting. Eminent physiologists have lately main- 
tained that the faulty nutrition which results in tubercle is 
caused by a deficiency of oily substances, and therefore 
such of these bodies as are easiest digested and absorbed 
have been indicated as remedies. Cod-liver oil has come 
into use for this purpose. Dr. Hughes Bennett, who first 



INJURIOUS EFFECTS OF BAD DIET. 40 7 

introduced this oil to the aotice of the public, states that 
butchers, cooks, oilmen, tanners, and others who are con- 
stantly coming in contact with fatty matter, are less liable 
than others to tubercular disease; and Dr.* Simpson has 
observed that children and young persons employed in 
wool-factories, where large quantities of oil are daily used, 
are generally exempt from scrofula and pulmonary con- 
sumption. These facts would indicate that even t lit 1 ab- 
sorption of fatty matter through the skin may power- 
fully influence nutrition. Dr. Bennett says that, to pre- 
vent consumption during youth, indulgence in indigestible^ 
articles of food should be avoided, especially pastry, unripe 
fruit, salted provisions, and acid drinks; while the habit 
of eating a certain quantity of fat should be encouraged, 
and, if necessary,, made imperative. 

Dr. Carpenter observes: "Then 1 is a strong tendency 
and increasing reason to believe that a deficiency of olea- 
ginous matter, in a state fit for appropriating by the nutri- 
tive processes, is a fertile source of diseased action, espe- 
cially that of a tuberculous character; and that the habitual 
use of it in largo proportions would operate favorably in 
the prevention of such maladies, as cod-liver oil unquestion- 
ably does in their cure." 

Dr. Hooker, in a report on the diet of the sick, says : 
" 1. Of all persons between the ages of lift ecu and twenty- 
two years, more than one-fifth eat no fat meat; 2. That of 
persons at the age of forty-five, all excepl less than one in 

fifty habitually use fat meat; 3. Of those who have ab- 
stained, a few acquire an appetite for it, and live t<> a good 

old ago, while the groat proportion die of consumption 
before forty-live; 4. Of persons dying of eonsumpl ion he- 

en the ages of fifteen and forty-five, nine-tenths, al least, 
have never used fat meat." 

461. Unwholesome Foods. — Articles of food differ in 
digestibility, some being readily dissolved and assimilated, 
while others are changed in the Btomach with such diffi- 



408 ELEMENTARY HYGIENE. 

culty as to irritate and injure the organ. Animal food is 
more easily digested than vegetable, as it represents vege- 
table food that has been already once digested, and its 
insoluble portions separated. But the chief cause of un^ 
wholesomeness in foods is their bad condition. The quali- 
ties which render them easily digestible within the system, 
make them readily changeable without it; hence their 
tendency to " spoil," and the facility of injurious culinary 
changes. Bread, sour and heavy from unskillful working or 
damaged flour, butter rancid and offensive, potatoes sodden, 
and meat tainted or diseased, are examples of unwhole- 
some diet, which produce disturbance in the system and 
often serious disease. Meat that has entered upon decom- 
position, or the flesh of diseased, immature, or over-driven 
animals, is unfit for use. They are liable to produce gastric 
disturbance and diarrhoea, or they may be actively and dan- 
gerously poisonous. 

462. Flesh Parasites. — The disease of the pig, known 
as " measles," is due to little parasitic animals which infest 
the flesh. When pork is thus affected, there are found 
scattered through the areolar or connective tissues numer- 
ous opaque or whitish points, which consist of little mem- 
branous bags, or cysts^ each containing a small embryonic 
animal, known as the Cysticercus cellulosus. These micro- 
scopic creatures are developed from the eggs of the com- 
mon tape-worm ^Taenia solimri). 

Dr. Klichenmeister fed a number of cysticerci to a crim- 
inal at different periods before his execution, varying from 
twelve to seventy-two hours, and, upon posterior tern ex- 
amination of the body, no less than ten young taenia were 
found in the intestine, four of which could be distinctly 
recognized as specimens of Taenia solium (Dalton). 

The cysticerci are sometimes found in the organs of the 
human body as well as in those of the lower animals. They 
are most likely to be met with in the voluntary muscles, 
but have been observed in the tissue of the heart, and, 






INJURIOUS EFFECTS OF BAD DIET. 409 

what is more remarkable, in Buch organs as the eve and 

brain. Their presence 4 in the muscles is not known to bt 
harmful, inasmuch as they have been found in considerable 
numbers in the muscular tissues of individuals who were 

accidentally killed while in a state of apparently perfect 
health. 

The Trichina spiralis is another parasite which infests 

the muscles of the pig, and is also found in those of the 
human subject. A muscle containing trichina 1 appears as 
if thickly beset with small whitish specks. Ench speck is 
in reality a cyst, which contains a single trichina, a minute, 
worm-like animal, coiled up in a spiral form. When straight- 
ened out, it measures about $*$-th of an inch in length, and 
about T oTr tli of an inch in diameter. Like the cysticerci, 
these animals find their way into the human stomach, and 
thence, by means of the circulation, to the muscles, where 
they occasionally exist in immense numbers. They have 
been discovered in the. muscles of persons who died by 
accident, and were otherwise apparently healthy; and also, 
and much more frequently, in subjects who have died from 
slow and debilitating disease. Within a few years past, it 

has been determined that the presence of these parasites 

not unfrequently a-ives rise to a peculiar disease, which has 
received the name of Trichiniasis. This affection is said to 

1 e highly febrile, often resembling typhoid or even typhus 
fever, and attended with excessive pain in the limbs, and 
oedema. 

In selecting meat, if the lean flesh looks speckled or 
blotched, it should be suspected. When the cysticerci are 

in great numbers, the flesh crackles as its fibres are cul 

across. The trichina', if inclosed within cysts, arc easily 
;i with the naked eye j but, if not, the microscope alone 

detects them. They may be effectually destroyed by thor- 
_h cooking. 



410 ELEMENTARY HYGIENE. 



CHAPTER XVIII. 

CLOTHING AND HEALTH. 

Section I. — Properties of Clothing Material. 

463. Purposes to be subserved. — The principal object 
of clothing being to defend the body against the effects of 
heat and cold, it is obvious that the qualities best suited 
to these purposes are what we are to seek in the selection 
of fabrics for wearing apparel in different seasons and cli- 
mates, and at different times. These qualities are chiefly 
connected w 7 ith the relations of fabrics to heat and moist- 
ure. The body is constantly losing heat both by conduc- 
tion and evaporation. In cold weather, the object is to 
prevent this loss as far as possible ; in warm weather it is 
desirable to promote it ; hence, we select our clothing with 
a view to these different purposes, wearing the free con- 
ductors and ready absorbers in summer, and the non-con- 
ductors and slow absorbers in winter. As far as is con- 
sistent with these primary objects, clothing should be light, 
durable, and readily cleansed. It should also be of such 
a character as will allow the free escape of the exhala- 
tions from the skin, and yet not be readily absorbent of 
moisture from without. Imperviousness is a very objec- 
tionable quality, and may, by retaining the cutaneous ex- 
cretions in contact with the body, lead to serious disease. 

464. Linen as an Article of Clothing. — This is a good 
conductor, and thus favors the escape of animal heat. It 
is also a rapid absorber of moisture from the surface of 
the body, and readily gives it off again by evaporation to 
the external air. For this reason, it produces a rapidly- 
cooling effect, even in hot weather, and is thus well 
adapted for summer use. It should not, however, under 



PROPERTIES OV CLOTHING MATERIAL. 4)1 

any circumstances, be worn next the skin, as it not only 

quickly cools the surface itself, but is incapable oi pre- 
venting- sudden chills from other causes. 

465. Cotton as an Article of Clothing. — Tins is a poorer 
'conductor of heat than linen, and consequently wanner. It 

is likewise less absorbent of moisture, and is therefore pref- 
erable for under-garments, or when it is desirable to avoid 
the cooling action produced by the evaporation of moist- 
ure from a material iti contact with the body. It ranks 
next to linen as a fabric for summer wear, being a much 
better conductor of heat and absorber of moisture than 
either silk or wool. 

466. Woolen as an Article of Clothing. — Woolen fab- 
rics, owing- to their coarseness and porosity, are capable of 
detaining- within their meshes considerable amounts of air, 
and this makes them slow conductors of heat. It is upon 
this property of imprisoning air within its interstices that 
the warmth of clothing in a great measure depends. The 
air itself is an excellent non-conductor of heat, and, when 
materials are worn which have the power of entrapping its 
particles, the body is virtually encased in a garment of air, 
and its heat thereby prevented from escaping. The denser 
the fibre atid the closer the texture, the less air there will 
be retained, and, hence, the cooler the clothing-. The con- 
verse is equally true, though to a more limited extent. In 
any clothing, if warmth is the object, the texture must be 
sufficiently close to prevent the passage of currents, but up 
to tin's point the more open it i<, the better. 

Woolens also possess a groat capacity f<>r moisture, 

though they take it up and give it out very slowly. This 

another valuable quality, giving- them great advantages 
as articles of clothing. Everyone may have noticed bow 

readily linen and cotton become wet, while woolen in the 

e length of time is scarcely more than dampened. The 

former will also drv rapidly, while woolen parts with its 

moisture at a much slower rate. It is, therefore, a better 



412 ELEMENTARY HYGIENE. 

protection against wet than either linen or cotton, and 
much warmer while wet, as the evaporation from its exter- 
nal surface is not nearly so rapid as from the surfaces of 
other materials. The water absorbed by different fabrics 
penetrates their fibres, and is also held between them in 
the interstices of the cloth. The latter can be wrung out, 
and is called water of interposition. The former is only 
got rid of by evaporation, and is termed hygroscopic water. 
Woolen greatly exceeds either linen or cotton in this power 
of hygroscopic absorption, taking up at least double the 
amount of water in proportion to its weight, and quadruple 
in proportion to its surface. 

" This property is a most important one. During per- 
spiration, the evaporation from the surface of the body is 
necessary to reduce the heat which is generated by exer- 
cise. When the exertion is finished, evaporation still goes 
on, often to such an extent as to chill the frame. When 
dry woolen clothing is put on after exertion, the vapor 
from the surface of the body is condensed in the wool, and 
gives out again the large amount of heat which had be- 
come latent when the water was vaporized. Therefore, a 
woolen covering, from this cause alone, at once feels w 7 arm 
when used during sweating. In the case of cotton and 
linen, the perspiration passes through and evaporates from 
the external surface without condensation ; the loss of heat 
then continues. These facts make it plain why dry woolen 
clothes are so useful after exertion." — (Parkes.) 

As an equalizer of the temperature and protector of the 
surface against sudden chills, wool stands at the head of 
all our usual wearing fabrics, and, when it can be tolerated, 
should be constantly worn next the skin. 

467. Color influences the relations of clothing to solar 
heat, though it does not affect it in regard to non-luminous 
heat, such as that emitted from stoves. Black clothes ab- 
sorb heat in a sunny day ; while white clothes reflect more 
of it. The power of absorption decreases as the shade 



MANNER OF DRESSING THE BODY. 41:> 

prows lighter. Thus, blaok absorbs the most, blue next, 
then green, yellow, and lastly white. Color also affects 
the relations of cloth to moisture, the darker-colored ma- 
terials absorbing more moisture than the light- colored. 
Black will absorb nearly as much again as white. 

Section II. — Manner of dressing tin Body. 

468. Its Importance. — Much more depends upon this 
than upon the materials used The best fabrics improperly 
put on may be the source of all sorts of diseases, while the 
p west, if used with judgment, are capable of conferring a 

dly degree of comfort. 

469. The Clothing should be li^ht. — All garments 
should be a-> light as is consistent with tin 4 main objects 
for which they are worn. Weight docs not necessarily 
imply warmth, and it often becomes a source of excessive 
fatigue and discomfort. Warmth is better attained by 
putting on several layers of light, loose-fitting garments, 
than fewer layers of heavy clothing. As before stated, it 
i- not the clothing itself, but the air imprisoned by it, 
which secures warmth; and the air is not only held within 
the meshes of the cloth, but a stratum is retained under- 
neath each additional layer of clothing 1 . It is, therefore, 
desirable to multiply the number of layers, which is only 
possible when light materials are used. 

470. It should be loose. — Every one knows that 1 
clothing is warmer than that which fits the body closely, 
and this alone should be sufficient reason for adopting it. 
Rut tight-fitting garments arc in other n very in- 
jurious. They obstruct the circulation, restrict the natu- 
ral motions and healthy exercise of the parts, and not 
unfrequently produce deformities of the worst character. 
Many have observed the effects of a tight-fitting head' 

gfl ii obstructing the flow of blood. Constricting the 
neck is even worse. The great veins which carry the 

blood from the head back to t:;e heart lie very Buperficially 



414 



ELEMENTARY HYGIENE. 






in the neck, and, when any thing tight is worn about this 
part, their currents are obstructed, and venous congestion 
of the brain results. 

471. Compression of the Chest and Abdomen. — It is, 
likewise, of the greatest importance that the motions of 
the chest and abdomen should not be interfered with. 
There is probably no part of the body where freedom of 




Fig. 120. 

A- diagram showing the natural form of the healthy chest, and the proper position of 
the organs which it contains. 

action and of circulation is more absolutely required than 
here. At the junction of the chest with the abdomen 
are located the lower portions of the lungs, the spleen, 
stomach, liver, etc. There are also given off from the 
aorta at this point several large vessels, which carry blood 
to the adjacent viscera. The diaphragm, the most impor- 
tant muscle engaged in the process of respiration, is like- 
wise found in this immediate vicinity. Every function of 
the body calls for the utmost freedom of movement in this 
important region. And yet it is the almost universal prac 



MANNER OF DRESSING THE B )DY. 



415 



tice among females to bind down these parts often to half 
their natural dimensions. Reference to Fig. 129 shows 
this to be one of the roomiest portions of the body when 
left in its natural condition. 

Fig. 130 shows the distortion which often results from 
compression. This deformity is not the worst of the evils 
which follow the practice of compressing these parts. The 
diaphragm is hampered in its actions, and the process of 
respiration thus directly interfered with. The lungs and 
heart are compressed, and the stomach and liver either 
forced out of place, or, what is worse, squeezed into much 




Fir,. 130. 
A dincmm showing the deformity produced by compression. 



less Bpace than they would naturally occupy. The portal 
circulation is thus obstructed, and the viscera, like the 
brain in the former case, become the scat of venous en- 
gorgement. 

It is hardly necessary f<» add that the troubles induced 

bv thifl -rate of things are of the most serious character. 



41G 



ELEMENTARY HYGIENE. 



Diseases of the liver, dyspepsia, and consumption, are 
among its legitimate and certain results, while other dis- 
orders of a less definite character are, no doubt, traceable 
to the same efficient cause. The compression, when early 
applied, as it usually is, finds the bones of the chest soft 
and yielding, so that they readily give way. If the con- 
striction is continued, as it is likely to be, for fear of losing 
" beauty of form," the bones, as age advances, harden and 
conform to the unyielding limitations without, and thus 
arise permanent and life-long deformity of the chest and 
continued restraint of its important organs. 

472. Compression of the Feet. — This is a common prac- 
tice, which often results in distortion and is always at- 
tended with great discomfort. Fig. 131 shows the de- 





Fig. 131. 



Fig. 132. 



formity produced by compression, while Fig. 132 gives the 
natural shape of the foot. In walking with the feet unre- 
strained, each foot, as it receives the weight of the bod} T , 
broadens slightly, and lengthens to the extent of half an 
inch or more. Freedom of motion in the foot itself is thus 
seen to be a natural requisite, and without it an easy, grace- 
ful walk is out of the question. Compression by the boot 
or shoe not only prevents this freedom of action, but also 
gives rise to deformity of the feet. The sole of the. boot 
should be as wide as and somewhat longer than the foot 



MANNER OF DRESSING THE BODY. 417 

when the weight of the body is resting upon it. The up- 
per-leather requires to be soft and yielding, and not so 
tight as to pinch the foot down upon the solo. The boot 
should be wide in front, leaving the toes perfect freedom of 

movement. It" too narrow, they are made to override each 
other, thus producing ingrowing toe-nails, corns, bunions, 

etc. The hods should be low and broad, so as to furnish 
a firm support. High heels throw the foot forward toward 

the point> ot' the boots, and tend to produce flattening of 
the arch o( the foot. 

473. Clothing should favor Uniformity of Temperature. 
— In health, all parts of the body have an av T erage tempera- 
ture of about 99° Fahr., and this is regulated and main- 
tained by the circulation of the blood. This uniformity of 
temperature throughout the body is of the utmost impor- 
tance, and, as it is controlled through the circulation, any 
thing which disturbs this should be carefully avoided. 
Clothing may do it in various ways, producing local results 
often of a very injurious nature. Compression obstructs 
the flow of blood, and at the same time forces out what 
the part already contains. It thus causes paleness of the 
parts, and is attended with an immediate lowering of the 
t niperature. Hence the cold feet and lian is, caused by 
tight boots and tight gloves. Over-clothing particular 
points lead- to the accumulation of heat and consequent 
relaxation of the vessels, when more than t he normal supply 
of blood flows in, and congestion results. A lack of cloth- 
ing, by affording insufficient protection, permits the rapid 

ape of heat, and thus the temperature may fall below 
the healthy standard, while the surface-blood is driven in- 
ward, producing congestion of the internal organs. Both 
these cau es of disturbance are generally operating: while 
pari i- overheated by a superabundance of clothing, 
another pari may at the same time be suffering from cold. 
This is often the case with children, who may he seen in 

• old weather loaded with clothing about the chest and 



418 ELEMENTARY HYGIENE. 

neck, while the legs and lower portions of the trunk are 
hardly more than covered. 

474. Disturbance of Vascular Parts. — Certain organs of 
the body are more vascular than others ; that is, their blood- 
vessels are larger and more numerous, and they receive a 
proportionately larger supply of blood. The throat, the 
lungs, the liver, and kidneys, are examples. Owing to 
their extreme vascularity, these organs are peculiarly liable 
to become the seat of engorgement if overheated by cloth- 
ing or otherwise, especially when other regions are at the 
same time imperfectly protected. The region of the kid- 
neys is commonly overdressed by the lapping at this point 
of the garments which clothe the trunk and lower extremi- 
ties. In this way, two or three extra thicknesses are com- 
monly obtained, and a tendency is thus created towards 
the accumulation of blood in these important organs. 

Muffling the throat is very common, particularly among 
children, and it is often remarked that those who wrap it 
the most are the ones who suffer most from its disorders. 
This practice is perhaps responsible for more sore-throats, 
coughs, and croups, than all other causes put together; and, 
when such overdressing of the neck is supplemented, as it 
commonly is in children, by short dresses and thinly-clad 
extremities, the conditions are most complete for the pro- 
duction of all sorts of throat and lung affections. 

475. Flannel next the Skin. — Uniformity of tempera- 
ture is greatly promoted by constantly wearing next the 
skin some non-conducting material, such as flannel or silk. 
This prevents sudden chilling of the surface, which, in our 
variable climate, is liable to take place at any time, unless 
specially guarded against. Flannel is found by experience 
to be best for this purpose ; but, in those cases w T here it 
irritates the skin, cotton-flannel or silk may be conveniently 
substituted. Linen should never be used. The good effects 
of wearing flannel next the skin the year round are un- 
questionable. In both cold and hot climates it is found to 



MAXXER OF DRESSING THE BODY. 419 

be an efficient safeguard against disease; and there are few 
who cannot soon become accustomed to its use. 

476. Clothing of Children, — Erroneous notions upon 
this subject lead to wrong practice, which is followed by 
the most pernicious consequences. Many entertain the idea 

that the constitutions of children may he hardened by ex- 
posure : hut, instead of any such vague benefit, specific and 

positive injuries are produced. Clothing, diet, and healthy 

growth, are intimately correlated. Food is the source of 
all bodily function and power, and tin 4 supply of force from 
this source is necessarily limited. Each day's bodily exer- 
cise, each day's mental exercise, each day's waste, repair, 
and growth i^ all the organs, and the definite amount of 
heat required to maintain the system at 99° during the 
twenty-four hours — each and all an 1 at the expense of the 
I daily digested, and any overtaxing in one direction 
involves corresponding deficiencies in others. If the body 
is insufficiently clothed, there is extra loss of power through 
waste <»f heat, and a necessary reaction upon the constitu- 
tion. The waste of heat entails a lowering of vital pro- 
cesses, and body and brain fail to reach a vigorous devel- 
opment. Thus, the naked legs and arms of children, which 
so please the vanity of silly mothers, are at the cost of their 

perfected «•< institutions. 

477. Clothing in Advanced Age.— As the bodily func- 
tions decline in rigor with advancing life, the protecting 

influence of clothing become more necessary. The incapa- 
bility of the aged to resi8t cold i- well known, and fatal 

iences frequently follow from persisting in old habits, 

and neglecting the indication- of Nature for increased 

warmth and abundance of apparel. 



420 ELEMENTARY HYGIENE. 



CHAPTER XIX. 

EXERCISE AND HEALTH. 

Section I. — Labor and Exercise. 

478. Man intended for Action. — Anatomy and Physi- 
ology alike proclaim that the purpose of the human con- 
stitution is activity. The provision for varied and complex 
movement is seen in the jointed skeleton, the contractile 
muscles, the controlling nerves, and the power-supplying 
apparatus of digestion and circulation. Thus the whole 
economy of the organism testifies that its end is action. 
Moreover, the circumstances of life involve the necessity 
of action. Effort must be put forth for the maintenance 
of existence, and for the gratification of the various facul- 
ties of our nature. 

479. Labor. — This great end of our being finds its legiti- 
mate and natural expression in labor, which is human action 
applied to various materials and objects, for the attainment 
of some productive or useful result. The necessity of labor 
is thus doubly provided for in the construction of the human 
fabric and the order of external Nature, and, when performed 
with due regard to the laws and rights of our being, it is 
in every respect a benefit and a blessing. But, when pur- 
sued to excess, as has unhappily been too common in the 
past history of mankind, it is perverted into degrading 
drudgery, and then becomes a curse. 

As skillful and effective labor involves intelligence, time 
and thought are needed to secure aptness in its perform- 
ance, and the narrower the range of effort, the greater is 
the facility attained. This restricts the individual to spe- 
cific pursuits, and gives rise to that diversified system of 
division of labor which has grown to such vast complexity 



EFFECTS OF REGULATED EXERCISE. 421 

in modern society. The tendency of this system is to call 
into intense exercise a portion — perhaps but a small por- 
tion — of the activity of the individual, and to leave the re- 
mainder of his powers unused. In many vocations the 
hands only are brought into requisition, while the body is 
unexercised; in others, the muscular system alone is in- 
volved, while the brain remains unoccupied; in other cases 
the brain is active and the body at rest, or perhaps a por- 
tion only of the brain is exerted, as in numerical computa- 
tion and managing accounts. 

480. Exercise.— Thus the tendency of modern life is to 
overwork a narrow portion of the human constitution and 
underwork the remainder, so that a large part of it is not 
called into the activity for which it was designed, and 
which is necessary to health. There are few persons whose 
habitual activities are so complete that they do not require 
to be supplemented by various artificial exertions, while 
this need is still more imperative with those of sedentary 
habits and the classes of leisure. To meet these various 
emergencies, and give to the unused portions of the human 
system their requisite action, is the object of exercise. 

Section II. — Effects of Regulated Exercise. 

481. Transformation of Physiological Forces, — All those 
vital processes which are essential to life, as digestion, cir- 
culation, respiration, secretion, are carried on independently 
of the will, and give rise to a large and constant amount 
of activity in the system. But labor and exercise are per- 
formed by calling into action an additional system of agen- 

— those of the voluntary muscles — and, to maintain 
these in a state of activity, involves an extra requisition 
upon the various involuntary organs. As the materials of 
tie- body air* derived from the substance of the food, so all 
vital power is derived tVom the force stored up in the food. 
j-;mic matter is in ;i state of molecular tension, and, when 
omposed, these tensions are given out in the form of 



422 ELEMENTARY HYGIEXE. 

physical forces. Food is organic matter, suited to under- 
go assimilation, and then to give out its molecular tensions 
in various forms, as animal heat, muscular power. It fol- 
lows that in work, or exercise, the voluntary muscular sys- 
tem draws upon the involuntary functions for its supply of 
energy ; and hence, in proportion to the force expended, is 
the general exaltation of the vital processes. 

482. Exercise, Waste, and Repair. — Bodily exertion thus 
increases atomic changes, and quickens that metamorpho- 
sis of tissue in which health essentially consists. Exercise 
is at the expense of waste; waste involves repair, and 
these augmented processes call into higher action the whole 
apparatus of supply and excretion. Habitual exercise is 
thus the cause and condition of that vital renovation of 
parts which is the source and measure of constitutional 
vi^or. 

483. Effect upon the Circulation. — As the circulation 
ministers immediately to all the functions, its energy rises 
and falls with their activity. Exercise increases the move- 
ments of the heart in both force and frequency, and acceler- 
ates the flow of blood through all parts of the body. The 
circulation is also aided by the contractions of the volun- 
tary muscles, which, by pressing upon the walls of the veins, 
tend to force along the current of blood. Moreover, this 
increased activity of the circulation meets the increased 
demand of the muscles for new material, to renew the disin- 
tegrated structures ; and it also effects the speedy removal 
of all waste products, by rapidly transferring them to the 
proper eliminating organs. Thus, the complex stream 
from which nutritive materials are constantly drawn, and 
into which waste matters are constantly poured, is directly 
affected, both in its composition and rate of movement, by 
the state of action of the voluntary muscles. 

Exercise also, it is well known, increases the produc- 
tion of heat. It is through the increased activity of the 
circulation that the body is warmed by exercise. This is 



EFFECTS OF REGULATED EXERCISE. 423 

the reason why walking is so effectual in warming the feet, 

and why exertion of any kind raises the temperature of the 
parts employed. 

484. Effect upon Respiration. — Circulation and respira- 
tion are accelerated together by exercise, as whatever quick- 
ens the pulse hastens the breathing. It being the office of 
respiration to furnish the prime mover of vital changes — 
oxygen — ami to rid the system of the chief product of such 
change — carbonic acid — this process is doubly subservient 
to the great dynamic objects of the organism. It follows 
that a fundamental condition of exercise is unimpeded res- 
piration. If the pulmonary circulation and the elimination 
oIl carbon are in any way interfered with, the power of con- 
tinued exertion rapidly declines. As thus muscular move- 
ment depends immediately upon the excretion of carbonic 
acid from the system, and as this, in turn, depends apon 
the state of the air itself, we see that an impure atmos- 
phere is unfavorable to vigorous and healthful exercise. 
This explains the lassitude and indisposition to effort in 
unventilated houses, workshops, and factories. Exercise 
should, therefore, as much as possible, be carried on in 
the open air, or in places which admit of the freest venti- 
lation. 

485. Effects upon Digestion. — As power comes from food 
in the case of the living machine, increased expenditure of 
power, of course, implies increased consumption of food; 
hence, exercise sharpens the appetite. In those who in- 
dulge in active and regular exercise, digestion is effected 
with greater ease, and the process is more rapidly and more 
thoroughly completed than in those of inactive habits. In 
many e:i-<-<. when- the digestive function 1ms become im- 
paired, either from habitual inactivity or a too close appli- 
cation of tti*- mind, relief can easily come through system- 
atic and judicious exercise. Inn Mediate exertion after a full 
meal i< injurious, for several roiMni^. The distended con- 
dition of the h interferes with the freemovemenl of 



424 ELEMENTARY HYGIENE. 

the diaphragm and heart, and thus both respiration and 
circulation are mechanically impeded, while the diversion 
of blood and nervous force to the muscles withdraws them 
from the digestive organs and hinders their functions. 

486. Effect upon the Skin. — With exercise, the skin be- 
comes redder and hotter, from the increased amount of 
blood it receives. During exertion, heat is rapidly devel- 
oped within the body, but its accumulation is prevented by 
the escape of water through the skin. No amount of exter- 
nal cold is able to prevent this outward passage of fluid, 
though it may slightly hinder evaporation. There is, there- 
fore, little danger of chill during active exercise ; but, when 
exertion is over, there is great danger of it, for the heat of 
the body rapidly declines, while evaporation continues, 
which still more reduces the temperature. During exer- 
tion, the skin may be exposed without danger ; but, during 
the intervals of rest, it should be covered sufficiently to 
prevent the least feeling of coolness of the surface. 

487. Exercise should be regular. — Like eating and sleep- 
ing, exercise should become a regular and persistent daily 
habit. It is an imperative necessity of the system, and, as 
an element of personal hygiene, is indispensable. If it be 
resorted to in any form of bodily training, as in military 
drill, rowing, or other athletic effort, it is found that the 
periods of exertion must not be less than half an hour, in 
order to take hold of the system, and produce the positive 
effect of bodily discipline. 

488. The Mind in Exercise. — Exercise, or simple muscu- 
lar movement, whatever may be its value for health, has in 
itself very few attractions, and will be avoided rather than 
practised, unless there is connected with it something capa- 
ble of calling the mind into pleasurable activity. When 
taken merely from a sense of duty, or " because the health 
requires it," exercise becomes a drag and a bore, without 
vigor and of little benefit. When, however, it can be made 
the means of enjoyment, by associating with it something 



EXCESSIVE AND INSUFFICIENT EXERCISE. 4i>5 

agreeable and exhilarating, it becomes at once spontaneous, 

vigorous, and hearty, and its value to the health, both of 
mind and body, is in a great degree increased. 

Section III. — Excessivi atul Insufficient Exercise. 

489. Effects of Over-exertion.— With the proper amount 
exercise, the muscles increase in size, hardness, and 

stic vigor, until the equilibrium of waste and repair is 
carried to its highest point. Exercise is at the expenseof 
the part in action; in vigorous exertion, decomposition 
prevails over renewal. The muscles can bear this for a 
certain length of time, and then demand rest, in which 
repair prevails over waste, and restores the balance. If 
exertion be pushed still further, the equilibrium is lost; 
destructive changes prevail over reparative, and the muscle 
begins to degenerate and lose powder. Prolonged exertion, 
without sufficient rest, impairs nutrition, and renders the 
muscular fibres soft and flabby. Nature thus provides for 
the rhythm of activity and repose. The involuntary mus- 
cles, as we have seen — those of the heart and chest — act in 
this intermitting way, and are thus kept up to a constant 
state of vigor. The law is equally imperative 4 lor the 
voluntary muscles, and the proper rest is to be secured 
either by ceasing from activity, or by calling different sets 
of muscles into alternate exercise. 

When the muscles are weak, repair goes on more 
slowly than when they are "in condition/' Hence, in any 
effort at acquiring strength by exercise, either after sick- 
ness or prolonged sedentary occupation, t he exercise should 

at first be very light, and of short duration, with long 

intervals of rest. A- the strength slowly increases, the 
exercise may be increased, bu1 exhaustion in all such cases 

i- t') be carefully avoided. 

Excessive exen i-<' often produces palpitation, and some- 
times hypertrophy and valvular d i-ease of the heart. Dur- 
ing exertion, if the heart it not oppressed, its movements, 



426 ELEMENTARY HYGIEXE. 

though rapid and forcible, are regular and equal ; but when 
it becomes embarrassed, the pulse- beats are quick, unequal, 
and at last become irregular, indicating injury to the organ. 
All great or sudden efforts should be avoided, as they not 
only affect injuriously the muscular system, by direct over- 
strain, but it is at such times that blood-vessels are ruptured, 
and that the walls of important cavities give way. 

Rest after exertion is one of the indispensable condi- 
tions of health. Work or exercise carried habitually to the 
length of exhaustion, by lowering the bodily vigor and de- 
pressing the powers of the constitution, not only diminishes 
resistance to the encroachments of disease, but greatly re- 
duces the capability of recovery in cases of sickness. 
Particularly in childhood, when the bones are yet incom- 
pletely ossified, and the muscles undeveloped, excessive 
labor or exertion is liable to entail permanent injury. If 
persisted in, arrested development of either body or mind 
can hardly fail to result. From the age of fifteen to twenty- 
five, although full growth may have been reached, the 
powers of endurance have not attained their maximum, and 
all exhausting tasks require to be avoided. Young soldiers 
break down under the toils and privations of the camp 
sooner than mature men. This is also true in civil life, 
where the young and immature are called upon to match 
their powers with those in the maturity of manhood ; and 
the remark is equally applicable to the female, under 
the spur of competition with the* male sex. The conse- 
quences are seen in broken-down constitutions and prema- 
ture decay. 

490. Effects of Insufficient Exercise. — Inaction contra- 
venes the supreme design of the human constitution, and 
is therefore adverse to its health. As bodily vigor results 
only from active and well-regulated exercise, the absence 
of such exercise must entail bodily debility. As exertion 
favors nutrition and the healthy development of active 
parts, inaction impairs nutrition, reduces the size of the 






EXCESSIVE AND INSUFFICIENT EXERCISE. 427 

muscles, and gives rise to feebleness. The amount of In- 
jury in the case may, however, depend much upon accom- 
panying circumstances. U abstinence 1 from exercise be 
attended by abstinence in diet, there will still be loss of 
power, low vitality, and diminished resistance to morbific 
influences; the evils will be rather of a negative character. 
But, if deficient exercise be accompanied by a free indul- 
gence of the appetite, perverted nutrition and positive dis- 
ease will be the necessary consequence. Nutritive mate- 
rials that would be reduced and excreted through bodily 
exertion, accumulate in the system., clogging its move- 
ments, deranging its functions, and deteriorating its struct- 
ures. Not only is there an abnormal accumulation of fat, 
amounting to actual disease, but a disturbance of the nutri- 
tive forces, that undermines the healthy structure of the 
tissues. Nor is this muscular deterioration limited merely 
to the parts that are unused ; the involuntary mechanism 
becomes implicated. Deficiency of exercise often leads to 
fatty degeneration of the heart, with loss of power and 
derangement of the circulation. In short, as vigorous and 
systematic exercise is a prime condition of the general 
health, so the want of it favors the approach of disease, 
which may take many forms, according to the circumstances 
of the constitution. 

491. Amount and Conditions of Exercise. — As to the 
amount of exercise necessary to meet the requirements of 
the healthy individual, no precise rules can be given; the 
quantity will vary with many circumstances. Persons of 
sedentary habits would be seriously injured by attempting 
to perform an amount of work which, to others of a mere 
active turn, would hardly exceed the bounds of reereath n. 
The inmate of the workshop or factory would be speedily 
exhausted by the ordinary tasks of the out-door laborer. 

In any given Case, the amount of exerei>e should be deter- 
mined and regulated by the state of the constitution. Thai 

exercise is deficient which docs Dot engage the vigorous 



428 ELEMENTARY HYGIENE. 

action of the chief muscles of the system for a considera- 
ble period each day ; and that too great which, passing 
beyond the point of simple fatigue, is prolonged to the 
period of exhaustion. 

The sedentary, if they would acquire strength, must 
begin with light exertion, limited to short periods, and 
take ample time for rest. Nothing is more erroneous, and, 
if carried into practice, more injurious, than the notion that 
great exertion will augment the strength of those unaccus- 
tomed to active exercise. The growth of muscle, in both 
substance and power, is a gradual process, and one that is 
retarded rather than hastened by overwork. If exhaustion 
or restlessness follows exercise, we may be certain that it 
has been overdone, and will be productive of weakness 
rather than strength. 

As has been stated in a previous chapter, an abundant 
supply of pure air is at all times a vital necessity of health ; 
but the demands of the system in this respect arc greatly 
increased during active muscular exertion. As the dimi- 
nution of waste products is a result of oxidation, it is 
hindered by breathing an impure atmosphere. For this 
further reason, open-air exercise is much superior, as a 
health-promoting agent, to that carried on within the walls 
of a gymnasium or other confined area. 

492. Remedial Influence of Exercise. — If exercise is an 
essential condition of health, and the want of it a fruitful 
source of disease, it is obvious that only by the reestablish- 
ment of the needed exercise can health be regained. But 
in many cases the diseases induced make the required 
effort either impossible or very difficult. What is known 
as the movement-cure is a kind of dynamic treatment, in 
which the patient is subjected by the physician to various 
kinds of artificial exercise. In many cases of local weak- 
ness and partial paralysis, by the help of skillfully-con- 
structed mechanical contrivances, these parts are gradually 
brought into action, and healthy power slowly recovered 






RELATIONS OF MIND AND BODY. 429 

The principle in this case is valuable, and, important as a 
remedial agency, its employment has accomplished much 
good, and more is to be expected from its further develop- 
ment. 



CHAPTER XX. 

MEXTAL HYGIENE. 

Section I. — Relations of Mind and Body. 

493. Mental Health a Physiological Question. — Thus 
far we have confined attention mainly to the influences 
which act on the bodily health, but the principles of 
hygiene have a still higher application. The mind has its 
states of health and vigor, of debility and disease, like the 
body, and these states are influenced by definite causes in 
the former case as well as in the latter. Mental philosophy, 
as commonly understood, explains to us the operations of 
thought and feeling as we discover them in the working 
of our own minds, and takes little account of the part 
played by the corporeal system in the control of these 
processes. But, if we would understand the conditions of 
mental health, and the* nature and causes of mental impair- 
ment, the body must at once be taken into account. The 
study of mental phenomena in their corporeal relations thus 
becomes the business of the physiologist. He sees thai 
mind is not only intimately dependent upon the body, bui 
that the two have close and powerful reactions; states of 
bodv determining conditions of mind, and Btates of mind 
influencing conditions of body. Nature presents the prob- 
lem, not of mind separate, but of mind and body bound ii|> 
in a living unity, and the physiologist must take the ques- 
tion as he find- it. 

494. The Brain and the Mind. — It is now universally 
admitted thai the brain i- the grand nervous centre of 



430 ELEMENTARY HYGIENE. 

thought and feeling — the material instrument of the mind, 
and that all mental actions are accompanied and con- 
ditioned by physiological actions. From the high com- 
plexity of composition of nervous matter, it is extremely 
unstable and prone to change. The brain is therefore not 
only, like all other parts of the body, subject to the double 
metamorphosis of waste and repair, but the transforma- 
tions take place in this organ with more rapidity than in 
any other part of the system. Upon these changes the 
mental operations are vitally dependent, and, if in any way 
they are interfered with, there is disturbance of the intel- 
lectual processes. If the cerebral circulation is lowered, 
mental activity is diminished; if accelerated, the mind's 
action is exalted. Various foreign substances introduced 
into the bl}od-stream alter the course of thought, some 
affecting it one way and some another, but each, through 
its specific action, producing characteristic psychological 
effects. Inflammation of the brain induces delirium, while 
different diseases of the organ, or perversions of the blood 
circulating through it, give rise to various forms of insanity. 
It is important to note, not only that mind and body 
are both governed by laws, but that they are to a great 
extent governed by the same laws. Whatever improves 
the physical qualities of the brain, improves also the mind ; 
whatever deteriorates the brain, impairs the mind. They 
have a common development, are equally increased in 
vigor, capacity, and power, by systematic and judicious ex- 
ercise, and are alike injured by deficient or excessive ef- 
fort. The brain is exhausted by thinking, as much as the 
muscles by acting, and, like the exhausted muscles, it re- 
quires time for the restoration of vigor through nutritive 
repair. As thus the mind is dependent upon the condi- 
tions of the brain, while the brain is controlled by the 
bodily system, we see how impossible it is to deal with 
the mental powers in a practical way, without taking the 
material organization into account. 



RELATIONS OF MIND AND BODY. 431 

495. Mental Health and Disease. — The observations 
made in regard to the true nature of disease (368, 369) — thai 
it is nothing more than perverted physiological action — 
d jed to be here repeated with emphasis. Those who ha- 
bitually think of the mind as a separate entity merely co- 
existing in some vague way with the body, will naturally 
look upon mental derangements as disorders of this entity 
— diseases of an abstraction. But this view has proved 
misleading and injurious in the extreme. So long as mala- 
dies of the mind were regarded as demoniac possessions, 
or as " fermentations taking place in a spiritual essence," 
all rational causality was excluded, and the arts of relief 
and prevention were impossible. When, however, it be- 
came established that mind depends upon definite physio- 
logical conditions, there was no escape from the conclusion 
that physiological perversions are causes of mental de- 
rangement. " Fair weather and foul equally depend upon 
the laws of meteorology ; health and disease equally de- 
pend upon the laws of animal life." As mental health is 
dependent upon the due nutrition, stimulation, and repose 
of the brain, mental disease is to be regarded as resulting 
from the interruption or disturbance of those conditions. 

In showing that mental weakness is a concomitant of 
bodily debilty, and mental aberration a consequence of 
bodily disorder, the physiologist lays the sure foundations 
of a practical M\ mtctf Hygiene^ the province of which is, to 

sider the various causes which disturb the harmony and 
impair the vigor of mental actions. Taking note of the 
multiplied forms and degrees of disturbance and degeneracy 
to which the mental nature of man is subject, it traces them 
to their numerous causes, and discloses the extent to which 
thev are avoidable. As bodily and mental health depend 

to a great <\(><sr<>(> upon the same eondit ions, all that has 

hem -aid in the foregoing chapters concerning the sanitary 
influences which affect the corporeal system has likewise 
it- bearing upon health of mind. Hut the mental aspects 



432 ELEMENTARY HYGIENE. 

of the subject are so generally overlooked as to demand 
special consideration. 

Section II. — Causes of Mental Impairment 

496. Insanity the Result of Concurring Influences. — As 

the organ of the mind is the most delicate and complex of 
all parts of the living system, while its manifestations are 
so varied as to comprehend the whole circle of human 
thought and feelings, it is natural to suppose that the 
causes of cerebral impairment will be varied and complex 
in an equal degree. These causes are usually regarded as 
twofold, moral and physical. The former are those which 
take effect through the mind, as anxiety, over-study, or 
reverses of fortune ; the latter are those which act directly 
upon the physical system without the intervention of the 
mind, as blood-poisoning by fever or narcotics, or an in- 
jury to the head. Another division is into predisposing 
and exciting causes. Predisposing causes are such as act 
remotely, or by slow degrees, to undermine the mental 
health; while exciting causes are those untoward events 
which immediately precede the breaking down of the mind. 
It is a common error to assign some shock or calamity 
as the efficient and adequate cause of an insane outbreak, 
whereas the real causality lies further back, and the occur- 
rence in question is only the occasion of its development. 
The germ of the insanity may have been deeply latent in 
the constitution, and a long train of influences may have 
been at work to impair the cerebral vigor, while some 
event, perhaps of slight importance in itself, serves to 
bring on the final catastrophe. When it is said that a per- 
son has become insane through disappointment or religious 
excitement, we are not to suppose that this is the whole 
statement : the question arises, How is it that others in 
quite similar circumstances are unaffected ? The human 
mind is not so constituted as to snap by a sudden strain, 
like cast-iron ; insanity suddenly produced by the action 



CAUSES OF MENTAL IMPAIRMENT. 433 

of a single cause is of the rarest occurrence. Only by a 
"conspiracy of conditions," internal and external, proxi- 
mate and remote, is the fabric of reason usually overthrown. 

We will tirst notice the immediate physiological actions 
by which health of mind is destroyed, and this will prepare 
us to understand how the remoter causes of mental impair- 
ment take effect. 

497. Nutrition of the Cerebral Structures.— If the mind 
is dependent upon the brain, it follows that each act of 
mind has its physical conditions, and this conditioning must 
of course be in accordance with the structure of the organ. 
The mental mechanism consists essentially of millions of 
cells and fibres, the former of which are the generators 
and the latter the transmitters of force. In thinking and 
feeling, these are called into exercise, and according to its 
intensity exhausted ; while their functional power is re- 
stored by nutritive assimilation. The structure of the 
parts being perfect, mental coherency, energy, and health, 
depend upon their perfect nutrition. On the other hand, 
disordered mental manifestations are due to incapacitated 
structures which are immediately caused by imperfect nu- 
trition. It is here, in their disturbance of the nutritive 
operations of the brain, that most of the causes of mental 
impairment take effect. " We attribute a large share of 
mental disease to pathological conditions of the brain whose 
most prominent characteristic is defective nutrition of the 
organ. In a very large proportion of cases this deficient 
nutrition is manifested after death in an actual shrinking 
of the brain — a shrinking which is coextensive with the 
duration and the degree of the loss of mental power. Tin.- 
loss of power marks nil instances of cerebral decay, and is 
consequently a condition of most chronic cases of excite- 
ment n ( Bucknill and Tuke). 

The effect of impaired nutrition is, to produce derange- 
ments of structure, and these take many forms in the vari- 
ous cas4 - "f cerebral disease. The microscope has done 



434 ELEMENTARY HYGIENE. 

much to elucidate the pathological changes of the brain, 
but such is the marvelous delicacy of the organ that micro- 
scopists are still intensely occupied in making out the sub- 
tle details of its normal structure. Many physical indica- 
tions of nervous disorder no doubt remain to be discovered ; 
but, from the peculiar complexity and difficulty of the case, 
a large amount of infirmity of nerve-element will probably 
never be detected by physical means. Nutrition results 
from a relation between nerve-tissue and the blood ; the 
causes of its perversion are therefore to be sought in vari- 
ous disturbances of the circulation as well as in the nerve- 
element itself. 

498. Disturbance in the Cerebral Circulation, — Nutrition 
is dependent upon the supply of blood ; in the brain, per- 
haps, more closely than in any other organ. The gray sub- 
stance of the cerebral convolutions, which are devoted to 
the higher mental operations, is richly supplied with minute 
blood-vessels which impart to the cells the material of their 
renewal, and remove the waste products of their activity. 
The quantity and quality of the blood they transmit must 
therefore exert a determining influence over the functions 
and health of the organ. 

499. Congestion and its Effects, — As mental action de- 
pends upon the interchange taking place between the blood- 
capillaries and the nerve-cells, it follows that increased ex- 
citation and interaction of ideas is accompanied by increas- 
ing interchange and demand for more blood. Or, if, from 
any cause, there is excessive brainward determination of 
blood, the plethora of the capillaries gives rise to increased 
mental excitement. 

If this heightened activity is prolonged beyond due 
limits, and especially if the brain is weakly organized, a 
state of morbid congestion is induced, and over-stimula- 
tion is followed by stagnation of ideas, head-swimming, 
and emotional depression and irritability. " There are few 
students who are not practically conversant with the slighter 






CAUSES OF MENTAL IMPAIRMENT. 435 

symptoms of cerebral congestion. Absorbed in some intel* 
lectual pursuit, the student's head becomes hot and painful, 
and his brain even feels too large for his skull. With ex- 
hausted powers of thought and attention, he retires at a 
late hour, as he hopes, to rest, but he lint Is that he cannot 
sleep; or, if he does, his repose is unrefreshing and dis- 
turbed by dreams. An hour's freedom from thought before 
retiring to bed would have enable* 1 the partly-congested 
brain to recover itself." 

The stagnation of the cerebral currents and imperfect 
removal of noxious products, with the irregularities of ex- 
citement and depression which are the results of frequent 
brain-congestion, produce defective nutrition, which tends 
to impair the soundness of the organ. 

500. Anaemia, or bloodlessness, the opposite state of 
congestion, produces similar mental effects. Insufficiency 
of healthy blood, whether caused by its actual loss from 
the system, or by poverty and dilution of the fluid through 
want of food, imperfect digestion, or any of the numerous 
anti-hygienic influences, by impairing the nutritive powers, 
enfeebles the organ and powerfully predisposes to insanity. 
In hyperemia, with hot head and fullness of the cerebral 
vessels, the mental functions are discharged with slowness 
and difficulty. In anaemia, with pale face, cool head, and 
weak pulse, the cerebral organs are in a state of irritable 
weakness, easily excited to action; the action, however, 
being powerless and irregular. 

"The blood itself may not reach its proper growth and 
development by reason of some defect in the function of 
the gland- that minister to its formation, or, carrying the 
Cause still further back, by rea>on of wretched conditions 

of life • there is, in consequence, a defective nutrition gener- 
ally, ag in scrofulous persons, and the nervous system shares 
in the general delicacy of constitution, so that, though 
quickly impressible and lively in reaction, it is irritable, 
feeble, and easily exhausted. In the condition of anaemia 



436 ELEMENTARY HYGIENE. 

we have an observable defect in the blood, and palpable 
nervous suffering in consequence; headaches, giddiness, 
low spirits, and susceptibility to emotional excitement, 
reveal the morbid effects. Poverty of blood, it can admit 
of no doubt, plays the same weighty part in the productu n 
of insanity as it does in the production of other nervous 
diseases, such as hysteria, chorea, neuralgia, and even epi- 
lepsy. The exhaustion produced by lactation is a well- 
recognized cause of mental derangement ; and a great loss 
of blood during childbirth has sometimes been the cause 
of an outbreak of insanity " (Dr. Maudsley). 

501. Perversions of the Blood.— Although the blood is a 
compound of wondrous complexity, and undergoing inces- 
sant change by active influx and drainage, yet in health its 
constitution is preserved in such exquisite balance, that the 
cerebral engine of thought and emotion is kept in harmo- 
nious and perfect action. This harmony is disturbed not 
only by excess or deficiency of the vital stream, but in a 
marked degree by the presence in it of various impurities. 
Every grade of mental disease, from the mildest depres- 
sion to the fury of delirium, may be produced by the accu- 
mulation in the blood of the waste matters of the tissues. 
The presence in the blood, for example, of unexcreted bile, 
so affects the nervous substance as to engender the gloomi- 
est feelings, from which the individual cannot free himself, 
although he knows that the cause of his depression is not 
in the actual condition of external circumstances, but is 
internal, and of a transient nature. But it only requires 
the prolonged action of this cause to carry this morbid 
state of nerve-element to that further stage of degeneration 
which shall result in the genuine melancholia of insanity. 
So also the non-evacuation of urinary products in the blood 
of a gouty patient acts upon the brain to produce an irri- 
tability which the mind cannot prevent ; and this, too, if 
not arrested by medical resources, is liable to pass on to 
maniacal excitement. 



CAUSES OF MENTAL IMPAIRMENT. 4:3 7 

In like manner, suppressed discharges, the morbid prod- 
ucts of typhus and typhoid fevers, the organic poisons 
generated in the system by small-pox ov syphilis, and not 
promptly eliminated, are often efficient causes of nutritive 
perversion in the brain which result in various forms of 
mental disorder. 

Various substances introduced into the blood, as opium, 
hashish, belladonna, take effect upon the brain, each per- 
verting the mental (unctions in a manner peculiar to itself. 
Ingested alcohol produces an artificial insanity, in which 
the various types of mental disease are distinctly mani- 
fested. Its first effect is a gentle stimulation and a mental 
excitement, such as often precedes an outbreak of mania. 
This is followed by a rapid flow of ideas, an incoherence 
of thought and speech, and an excitement of the passions, 
which disclose automatic disturbance and diminished vol- 
untary control, as in delirium from other causes. A con- 
dition of depression and maudlin melancholy succeeds, as 
convulsion passes into paralysis — the last scene of all being 
one of dementia and stupor. 

502. Nutritive Repair of the Brain —But, independent 
of the quantity or quality of the blood supplied to the 
brain, that organ is liable to certain conditions of exhaustion 
and nutritive degeneracy to an extent far greater than the 
other organs of the body. These other organs have vari- 
ous mean> of escape from overtasking; if they cannot in- 
crease their power so as to endure the burden imposed, 
they can refuse to act. Of throw th - of labor upon 

ie other part Overworking the stomach destroys ap- 

itr, and the task i- no longer imposed If the muscular 
system is worked beyond it< power, it does not itself break 
down, but the excessive strain i- thrown upon the nervous 
stem, which receives the injury. The overtasked lungs 
throw part of their burden upon the skin and liver, and the 
overworked liver is relieved bv the kidneys, Bui the econ- 
omy of the organism afford- the brain no vicarious relief; 



438 ELEMENTARY HYGIENE. 

if overburdened, it must suffer alone. Excessive exertion 
of the brain produces an excitement, which, instead of ceas- 
ing, is augmented by the very debility which it causes. 
The exhaustion continues the overwork, which again in- 
creases the exhaustion. The degeneration of nerve-ele- 
ment thus proceeds at a rapid rate of increase, which 
results in permanent perversion and degradation of the 
mental functions. 

The conditions of rest and nutritive renovation of the 
mind's organ are provided for in the mechanism of the 
solar system, by which the quietude of night, darkness, and 
silence alternates with the stimulation of light and day. 
The recovery of its tone through nutritive repair undoubt- 
edly takes place in the brain during the suspension of its 
functional activity in sleep. That sleep should be sound 
in quality and sufficient in quantity is one of the first con- 
ditions of mental health and vigor, and the want of it, as 
all have observed, reacts powerfully upon the state of the 
feelings. " The ill effects of insufficient sleep may be wit- 
nessed on some of the principal organic functions ; but it 
is the brain and nervous system that suffer chiefly and in 
the first instance. The consequences of a very protracted 
vigil are too well known to be mistaken ; but many a per- 
son is suffering, unconscious of the cause, from the habit 
of irregular and insufficient sleep. One of the most com- 
mon effects is a degree of nervous irritability and peevish- 
ness which even the happiest self-discipline can scarcely 
control. That buoyancy of the feelings, that cheerful, 
hopeful, trusting temper, which springs far more from 
organic conditions than from mature and definite convic- 
tions, give way to a spirit of dissatisfaction and dejection ; 
while the even demeanor, the measured activity, are re- 
placed either by a lassitude that renders any exertion pain- 
ful, or an impatience and restlessness not very conducive 
to happiness." 

Such are the effects "upon the healthy constitution of 



CAUSES OF MENTAL IMPAIRMENT. 439 

that slight disturbance of brain-nutrition which accompa- 
nies insufficient repose ; hut, when this state of things is 
much protracted or takes effect upon a weakly-organized 
nervous system, the mental integrity becomes endangered. 
Sleeplessness is both a symptom and an immediate cause 
of cerebral disorder. Bucknill and Tube observe: "Want 
of refreshing sleep we believe to be the true origin of in- 
sanity dependent upon moral causes. Very frequently, 
when strong emotion leads to insanity, it causes in the first 
instance complete loss of sleep." 

The quality of the sleep, moreover, that is, whether it 
be total or partial, is of the first importance. In painful 
and harassing dreams the emotional perturbation contin- 
ues, and the individual awakens exhausted rather than 
invigorated. It is probable that in such cases, when the 
mind is abandoned to fantasy, and the control of the judg- 
ment is lost, the wasteful activity of certain parts of the 
brain may exceed that .of the waking state. Various cases 
are mentioned in which patients have ascribed their attacks 
of mania to the influence of frightful dreams. 

We thus see in what mental impairment, in its various 
degrees, really consists. To the physiologist the question 
of healthy mental activity resolves itself into that of the 
soundness of nerve-element, and of the vigor and complete- 
ness of nutrition ; while mental impairment is seen to 
result from instability of the nerve-structures consequent 
upon defective nutrition. In this view, therefore, all 
causes, physical or moral, immediate or remote, which influ- 
ence the nutritive operations of the system, have a bearing, 
more or less dir ot, upon mental conditions and characfe r. 

We will now pass to Bome of the remoter influence - by 
which mental health is impaired. 

503. Hereditary Transmission. — The living constitution 
i- powerfully influenced by many slow-working agencies* 
The causes of mental deterioration produce effects in time, 
and through successive generations. Hereditary transmis- 



440 ELEMENTARY HYGIENE. 

sion thus becomes a leading factor in the problem of men- 
tal impairment, and accounts for many of the agencies by 
which it is produced. 

Bodily defects and diseases are transmissible. Con- 
sumption, gout, asthma, cancer, leprosy, scrofula, apoplexy, 
unsoundness of teeth, and even long-sight, short-sight, and 
squinting, are liable to be inherited. Of course these diseases 
are not transmitted in all cases of their occurrence, nor do 
they always psss directly from parent to offspring; one or 
two generations may be skipped, and the malady appear in 
the distant descendants. Hence, strictly speaking, it is not 
the disease that is hereditary, but a predisposition to it, 
which may either be neutralized and disappear, remain dor- 
mant, or break out, according to circumstances. 

There is, perhaps, no form of constitutional defect more 
markedly hereditary than morbidities of the nervous sys- 
tem. Esquirol observes that, of all diseases, insanity is the 
most hereditary. The proportion of cases in which this 
malady is ascribed to predisposition has been variously 
estimated at from one-fourth to nine-tenths ; probably at 
least one-half of all these cases of disease have this origin. 
Extensive and careful inquiry has led to the conclusion that 
predisposition to insanity on the part of the mother is more 
liable to be transmitted to children than a like tendency 
on the part of the father, but it is the daughters that are 
most exposed ; the maternal defect, while it is equally dan- 
gerous to the sons as the paternal, is twice as dangerous 
to the daughters. 

The common notion, that insanity is inherited only 
when madness in a parent reappears as madness in the 
child, is a most serious error. That which is transmitted i9 
nervous infirmity, which may assume an endless variety of 
forms. Parental nervous defect may issue in one membei 
of the family in unbalanced character, which is manifested 
in violent outbreaks of passion and unaccountable impulses, 
while another may go smoothly through life without exhib- 






CAUSES OF MENTAL IMPAIRMENT 441 

itiug a trace of it, and a third will break down into mania 
upon some try ing emergency. As features are modified by 
descent, so are diseases, and none assume so wide a diver- 
sity of aspect as those of the nervous system. 

"If, instead of limiting attention to the individual, we 
scan the organic evolution and decay o( a family — proces- 
ses which, as in the organism, arc sometimes going on si- 
multaneously — then it is made sufficiently evident how close 
are the fundamental relations of nervous diseases, how arti- 
ficial the divisions between them may sometimes appear* 
Epilepsy in the parent may become insanity in the off- 
spring, or insanity in the parent epilepsy in the child ; and 
chorea or convulsions in the child may be the consequence 
of great nervous excitability, natural or accidental, in the 
mother. In families in which there is a strong predispo- 
sition to insanity, it is not uncommon to find one member 
afflicted with one form of nervous disease and another with 
another; one suffers, perhaps, from epilepsy, another from 
neuralgia or hysteria, a third may commit suicide, and a 
fourth become maniacal. General paralysis is a disease 
which is usually the result of continual excesses of one sort 
or another; but it may unquestionably or-cur without any 
marked excesses, and when it does so there will mostly be 
discoverable an hereditary taint in the individual" (Dr. 
Ifaudsley). 

504. Debilitated Stock a Source of Criminality. — How 
the running down of stock through loss of vital power by 
hereditary influences should swell the ranks of the depend- 
out classes, or those incapable of self-support, is obvious; 
but this cause is equally powerful in reinforcing the dan- 
gerous who fill our jails and prisons. Immoral 
training and vicious associations lire undoubtedly among 
the potent agencies by which these are educated for a 
career of vice and crime, bui ;« cooperating cause of far 
greater power is low organization or defective cerebral 
end owm e nt They begin life with a nervous system inca* 



442 ELEMENTARY HYGIENE. 

pable of the higher controlling functions. The children of 
paupers generally inherit a lack of bodily and mental vigor, 
while the offspring of criminals have transmitted to them a 
disturbed balance of constitution — an activity of certain 
propensities, with a congenital weakness of the restraining 
sentiments. Upon this point a writer of large observa- 
tion and experience of these classes, Dr. S. G. Howe, ob- 
serves : 

" There is a common opinion that in classes and indi- 
viduals of low organization the purely animal appetites are 
apt to be fierce and ungovernable, but it is not so : on the 
contrary, as a general rule, the whole nature is let down 
and enfeebled ; and persons in this condition are docile and 
easily governed. Sometimes, indeed, there is fearful ac- 
tivity of the animal nature in persons of very low organi- 
zation, which impels them to commit shocking outrages ; 
but these are exceptional cases, and the passions are usu- 
all} 7 the consequences of drink, or of insanity, rather than 
of intensity of nature. As a rule, in the classes marked by 
low and degenerate organization, the animal instincts and 
impulses are not stronger than in the others. On the con- 
trary, the classes of higher bodily organization and vigor 
have more fire and potency even of animal appetites ; and 
their superiority comes, not from lack of impulses and temp- 
tations, but from greater activity and power of the restrain- 
ing faculties of reflection and of conscience." 

In the light of these facts, the causes of mental impair- 
ment acquire a new and startling significance. The vari- 
ous agencies which are adverse to health not only shorten 
the duration of life, but they degrade its quality ; while 
deteriorated life involves debilitated intellect and perverted 
moral powers. The general causes of impaired health 
which have been noticed, impure air, overcrowding, bad 
water, insufficient food, exposure to weather from inade- 
quate clothing, want of exercise, or exhausting labor, and 
the whole array of bad physical conditions, by undermining 






CAUSES OF MENTAL IMPAIRMENT. 443 

the bodily vigor and lowering the nutritive operations, be- 
come powerful and extensive causes of mental impairment, 
and stand in close relation to the evils and vices of society. 
Their baneful influence, however, is not measured by their 
immediate effects upon the individual; their power is mul- 
tiplied by transmission, for they inflict upon his posterity 
the curse of a bad descent. Evil habits and bad condi- 
tions of life may not in the first case reach the extent of 
mental derangement, but they so impair the vital stamina 
that their victim bequeathes to his children enfeebled and 
degenerated nervous organizations, which are incapable of 
withstanding the strains and shocks of social experience. 
The lowered vitality and perverted nutrition of the parent 
become feeble-mindedness or insanity in the offspring. 

Hence, " for the moral and intellectual elevation of the 
race, we are to look not exclusively to education, but to 
whatever tends to improve the bodily constitution, and 
especially the qualities' of the brain. In our schemes of 
philanthropy we are apt to deal with men as if they could 
be moulded to any desirable purpose, provided only the 
right instrumentalities are used; ignoring altogether the 
fact that there is a physical organ in the case, whose origi- 
nal endowments must limit very strictly the range of our 
moral appliances. But, while we are bringing to bear upon 
them all the kindly influences of learning and religion, lot 
us not overlook those physical agencies which determine 
the efficacy of the brain as the material instrument of the 
mind" (Dr. Kay). 

505. Overtasking the Emotions. — Increase of insanity 
i< undoubtedly a concomitant of advancing civilization. 
Th _■■ state is marked by simple and unchangeable 

ial institutions, uniformity of manners and habits, lim- 
ited wants, the discipline of privation, imperturbable resig- 
nation, feeble affection, and few emotions, The Bavi 

rarely laughs and rarely sheds tears. The mental disor- 
ders to which he is liable correspond to his fanperf 



444 ELEMENTARY HYGIENE. 

development ; they are idiocy and imbecility — the mental 
diseases of children. On the contrary, in the civilized state 
there is a high and varied development of the emotions : 
all the circumstances of refined society conspire to inten- 
sify the feelings. Pride, ambition, fear, grief, domestic 
trouble, speculation, reverses of fortune, great successes, 
and great failures, exemplify the excitement and intoxica- 
tion of the emotions to which a highly- civilized people are 
continually subjected. In this country the intense and 
universal passion for wealth, the periodical convulsions of 
politics, and the stimulation of free competition for place 
and profit, carry to a high point the strain upon the feel- 
ings. Worse than all, our education, instead of being a 
training to self-control, and a systematic discipline of the 
emotions through a calm cultivation of the sciences of Na- 
ture, is too generally conducted in the same spirit of ex- 
citement : studies are pursued under the spur of sharp 
competition for the prizes and applause of public examina- 
tions, and, in place of sober and solid attainment, our cult- 
ure degenerates into a mere preparation for trade and 
politics. This state of things is far from favorable to men- 
tal stability. The victims of overtasked and perverted 
emotion fill our asylums, and it is impossible to view the 
increasing tendencies to social and public excitement with- 
out grave solicitude for its future effects. 

506. Overtasking the Intellect. — This is an extensive 
cause of mental derangement, though perhaps less so than 
that just considered. The baneful effects of cerebral ex- 
haustion have already been noticed (502), and that study 
is often carried to this injurious length is notorious. Mod- 
erate use undoubtedly develops and strengthens the brain, 
and it is equally certain that, if the amount of work is car- 
ried much beyond this point, the organ is endangered. 
Among the causes of insanity tabulated in insane-asylum 
reports, excess of study figures as an inconsiderable item ; 
but this belongs to the class of causes which mainly act by 



S - OF MENTAL IMPAIRMENT. 445 

paving the way to a mental break-down. Oases like that 
of Hugh Miller, where, after an intense and pr< 

:n. the bra: _ by no means infre- 

:jt; but in i: - riilcl or overworked 

ient there may - - <»f future m< 

tal - le some other circui sfl of 

res:. _ se the £ ger- 

minate, and itself be t - the cause, whereas it is in 

realitv only the occasion. 

It lias been objected to this thai the lunatic 

lums are chiefly peopled with inferior rather than highly- 
cultivated minds; but inferior minds are just those n - 
likely to be injured by excessive study. The more highly 
developed the brain, the greater is endur- 

ance. In rncnv before the Parliamentary School 

;ter announced his conviction, as 
phv- _ sf who had specially studied the q\ iat 

the children of the educated class - ure capable, without 
injurv. of twice as many hours of school-study as the chil- 
dren of the uneducated ssea 

What amount of labor the brain will endure wit: 
overstraining, depends upon various con 
agf. _ a -its as 1 

ex* of application. The fa the 

adult will bear, unharmed, an amom or which would 

be most injuri- si _ person, and men of 

lore, without fatigue, mental applies:' 
which would be dang 
ho se brain-work 

_an will endure witl ntal lal 

ith- 

om apparent injury to the brain; but in 

lack 

beahhfu kind of 

led to the fa 



446 ELEMENTARY HYGIENE. 

by successful brain-workers who have achieved eminence 
in the various departments of mental activity. The col- 
lated results, however, have little value, for in the first 
place no one doubts that the cultivated brain is capable of 
a vast amount of labor, extending through a long lifetime, 
if judiciously exercised. In the second place, the biog- 
raphies of eminent brain - workers actually show a vast 
amount of ill health and suffering due to excessive study, 
while the number of those who achieve distinction as 
thinkers, and then pass to premature graves as a con- 
sequence of it, is by no means small ; and, in the third 
place, such a report is necessarily one-sided, as it deals 
only with the successes, and takes no account of the mul- 
titudes of failures of which the world never hears. 

It is not to be forgotten, however, that there are evils 
of mental under-action as well as of over-action. While 
there is no evidence that in the case of uncultured savages 
the brain is liable to become diseased from lack of exer- 
cise, the same thing cannot be affirmed of the cultivated 
races. The progress of civilization in these races is ac- 
companied by a higher development and increasing com- 
plexity of cerebral organization, and this higher condition 
can only be maintained by a correspondingly higher degree 
of functional exercise. Without that activity which its 
greater perfection implies and requires, the brain of the 
civilized man degenerates. A well-constituted organ de- 
mands exercise, and there can be no doubt that pleasura- 
ble, productive brain-work can be pursued to a great extent, 
in the form of close and severe mental labor, without in- 
jury. It is the evil accompaniments that generally work 
the mischief ; the poisoning of the blood in the stagnant 
air of close, un ventilated apartments ; the resuming of 
work directly after dinner, and prolonging it into the late 
hours of the night ; the provocation of stimulants and 
irregular habits ; the hard, repulsive taskwork continued 
without recreation , and the unrelieved tension of anxiety 



CAUSES OF MENTAL IMPAIRMENT. 44 7 

that frets and strains and softens the delicate gray matter 
of the brain, and ends at last in paralysis or imbecility, 

507. Early Symptoms of Mental Impairment. — Of all 
the calamities to which man is liable. Done is bo appalling* 
as the loss oi reason, and, when the diseases which cause 
it are far advanced, they are mostly beyond the reach of 
restorative measures. Bui a calamity so terrible does nol 
come unheralded. Mental disease has its gradual begin- 
ning — its period of incubation, as physicians term it — 
which is accompanied by various signals of impending dif- 
ficulty; and it is important that these early indications 
should be understood by all. 

One of the greatest warnings of approaching cerebral 
disease is debilitated attention and loss of memory. When 
an individual begins to fail in his customary power of 
keeping his mind to a subject, or forgets the names of 
familiar persons and objects, or is unable to make simple 
numerical calculations with his usual facility and accuracy, 
or oddly transposes his words in conversation, there is 
serious ground for apprehending softening of the brain or 
apoplectic seizure. Slight deviations of the facial features, 
the trifling elevation of an eyebrow, the drawing aside of 
the mouth a hair's breadth, or a faint faltering of the speech, 
are dangerous intimations of tin 1 advance of paralysis. 

The more active forms of mental disease have also 
their early symptoms. Preternatural acuteness of the 
causing exaggerations of sight, hearing, and smell, 
i< the frequent precursor of a maniacal outbreak. The 
sensibility is not only exalted, so that the individual s- 
hears, feels, and smells more keenly than in health, but it 

ften vitiated ; he Bees double, agreeable <>d<»r< become 

disgusting, and pleasant tastes offensive. A prickling 

n, or a Bense of coldness, or grittiness in thii 
touched, is sometimes experienced In the case of a man 
who died of apoplexy, there was for some time previous to 
hi.- ilhi' ling in both hands as if the skin were cov- 



448 ELEMENTARY HYGIENE. 

ered with minute and irritating particles of dust and sand. 
The approach of mental disease is also foreshadowed in 
the conduct. Singularity or eccentricity of deportment 
is not, in itself, to be taken as evidence of mental aliena- 
tion. A large margin must be allowed for individual pe- 
culiarities ; there are naturally crooked sticks as w^ell as 
straight ones. Whatever be the bent of the character, it 
is in the deviations from it that we are to watch for evi- 
dence of morbid action. When a person, who is well 
known to a circle of friends, begins to manifest unaccount- 
able singularities of behavior ; when a quiet and modest 
man becomes noisy and boastful; when a cautious man 
begins to embark in wild and reckless schemes ; when 
a person of a serious turn suddenly becomes hilarious, 
or one of a lively and buoyant disposition sinks into 
despondency; w^hen an affectionate person turns jealous 
and suspicious with no apparent reason, or one of usually 
steady, industrious habits becomes idle, neglectful of busi- 
ness, and takes to running about — in such cases there is 
reason to believe that trouble is brewing. These devia^ 
tions from customary habits " are the switch-points which 
indicate that the mind is leaving the main line, and that, 
if left to itself, it will speedily career to destruction." 

Sometimes the earliest symptoms of cerebral derange- 
ment are manifested in the consciousness itself, and, while 
no indications of disorder are disclosed in the outward 
behavior, the individual finds himself becoming the victim 
of morbid thoughts, w^hich he cannot banish. A patient, 
writing to Dr. Cheyne, observed : "lam not conscious of 
the decay or suspension of any of the powers of my mind. 
I am as well able as ever I was to attend to my business. 
My family suppose me in health ; yet the horrors of a 
mad-house are staring me in the face. I am a martyr to a 
species of persecution from within, which is becoming in- 
tolerable. I am urged to say the most shocking things ; 
blasphemous and obscene words are ever on my tongue." 



CAUSES OF MENTAL IMPAIRMENT. 449 

508. Hints and Precautions. — It is a serious error to 
suppose that, because there may be a predisposition to 
insanity in a family, therefore the members of it are to 
regard their danger in the light of a fatality from which 
there is no escape ; on the contrary, these aie preeminently 
the eases in which, to a wise discretion, forewarning is 
forearming. The instances are probably very few in which 
latent tendencies are developed into actual disease in spite 
of all precaution. It will generally be found that tin 1 out- 
break is due to some immediate disturbing agency which 
might have been avoided. 

Where such a tendency exists, the education, occupa- 
tion, and habits, should be ordered with the strictest refer- 
ence to it : the establishment of strong bodily health should 
be a paramount consideration. The physical education 
should be specially directed to strengthen the nervous sys- 
tem and diminish its excitability. Much study, bodily in- 
action, confinement to warm rooms, sleeping on feathers, 
are all favorable to undue nervous susceptibility. 

In the education of children thus circumstanced, that 
is. in their brain-exercises, it is of the first importance to 
remember that whatever tends in any degree to impair the 
mental health, acts with redoubled power when cooperat- 
ing with morbid tendencies. While the brain is vet plastic 
and pliable, a little mismanagement — the hum< ring of pre- 
cocity, the repression of physical and nervous activity, or 
over-stimulation of thought — may awaken the germs of 
mental disorder, and lead to the most injurious conse- 
quen 

To thus predisposed, steady and agreeable oc- 

cupation, which does not try the patience Of the temper, 
or involve much responsibility, excitement, or exhaustion, 
is in the highest degree d ttirable. Religious, political, 
and reformatory gatherings, where the passions are aroused 
and the sympathies excited, Bhould be carefully avoided, 
together with all excitements which tend to disturb the 



450 ELEMENTARY HYGIENE. 

sleep. In respect to the mental habits, in such cases, Dr. 
Ray has the following excellent practical suggestions : 

" Persons predisposed to mental disease should carefully 
avoid a partial, one-sided cultivation of their mental pow- 
ers — a fault to which their mental constitution renders 
them peculiarly liable. Let them bear in mind that every 
prominent trait of character, intellectual or moral, every 
favorite form of mental exercise, is liable to be fostered at 
the expense of other exercises and attributes, until it be- 
comes an indication of actual disease. Here lies their 
peculiar danger, that the very thing most agreeable to 
their taste and feelings is that- which they have most to 
fear. 

" There is another disposition cf mind to be carefully 
shunned by the class of persons in question — that of allow- 
ing the attention to be engrossed by some particular inter- 
est to the neglect of every other, even of those most nearly 
connected with the welfare of the individual. The caution 
is especially necessary in an age whose intellectual char- 
acter is marked by strife and conflict, rather than calm 
contemplation or philosophical inquiry ; and in which even 
the good and the true are pursued with an ardor more in- 
dicative of nervous excitement, than of pure, unadulter- 
ated emotion. The prevalent feeling is, that whatever is 
worth striving for at all, is worthy of all possible zeal and 
devotion ; and, supported by the sympathy and cooperation 
of others similarly diposed, the coldest natures become, at 
last, willing to go as far and as fast as any. 

" Where the mind of a person revolves in a very nar- 
row circle of thought, it lacks entirely that recuperative 
and invigorating power which springs from a wider com- 
prehension of things, and more numerous objects of in- 
terest. The habit of brooding over a single idea is calcu- 
lated to dwarf the soundest mind ; but, to those unfortu- 
nately constituted, it is positively dangerous, because they 
are easily led to this kind of partial mental activity, and 



CAUSES OF MENTAL IMPAIRMENT. 451 

are kept from running into fatal extremes by Done of those 

conservative agencies which a broader discipline and a 
more generous culture naturally furnish. The result of 
this continual dwelling on a favorite idea is, that it comes 
up unbidden, and cannot ho dismissed, at pleasure. Rea- 
son, fancy, passion, emotion — every power o( the mind, in 
short — are pressed into its service, until it is magnified 
into gigantic proportions and endowed with wonderful 
attributes. The conceptions become unnaturally vivid, 
the general views narrow and distorted, the properties of 
time and place are disregarded, the guiding, controlling 
power o( the mind is disturbed, and, as the last stage of 
this melancholy process, reason is completely dethroned." 

509. Medical Management. — Although diseases of the 
higher nervous centres, when they become seated, are, to 
a great extent, incurable, yet, in their incipient stages, 
they are in most eases quite amenable to treatment. But, 
unhappily, those instances where delay is fraught with the 

Ltest danger, are, of all others, most liable to be neg- 
lected in their earlier stages. If the liver or the lungs 
out of order, there is usually ineontinent haste to 
consult the physician; but, if the organ of reason is in 
danger of giving way, a mystery is made of it, and the 
dictates of common-sense are unheeded. 

r i> mer^ neglect the worst aspect of the ease; false 
notions of delicacy frequently become hinderances to early 
and decisive action. The ancienl superstition, which con- 
nected insanity with special Providential disfavor, descends 
to us in the shape <>f prejudices which speak of it still as a 

** taint. n and lead to a culpable obliquity in dealing with it. 

Physicians of the largesl experience attesl that, even when 
they are consulted in these cases, there is often the great- 
difficulty in getting at the real conditions, both the 
patient and his friends studiously concealing or flatly deny- 
ing the facta 

The progress of medical science and the impulses of 



452 ELEMENTARY HYGIENE. 

public philanthropy have called into existence those noble 
institutions where alone physical and moral medication 
can be best united, and which are generally administered 
by physicians of the largest experience in this department 
of practice. When, therefore, an individual begins to 
manifest symptoms which excite the apprehensions of his 
family or friends, no time should be lost in procuring the 
best professional advice and securing the advantages 
which those establishments offer ; and ,if the patient is 
placed in an asylum, the friends, remembering that time is 
generally an all - important element of recovery, should 
largely trust the discretion of the medical superintendent 
in regard to the proper duration of his confinement. 



QUESTIONS, 



PART FIRST. 

CHAPTER I. 

1. How are the bodily actions studied ? 

2. What tacts may we thus obtain ? 

3. Describe the ice-chamber experiment. What does it show? 

4. How ifi the Strength restored and the loss made gOOtl? 

5. In what form is matter excreted from the body? 

6. What is said oi the absorption of oxygen ? 

7. What is meant by the physiological balance? 

8. How may it be maintained V What conditions disturb it V 

9. What determines the amount of force set tree ? 

1<». Give an outline of the bodily structure. What is meant by bi- 
lateral symmetry 1 

11. Describe the vertebral column. What cavities do the bodies of 
the vertebra separate ? 

12. What doe- the spinal cnnal contain ? How is the ventral cavity 
divided? What canal traverses the two ventral chambers? What else 

the abdom< n cont li'i ? What the thorax 1 

13. Describe the h< ad. What arc contained within its cavities y 

14. What does a longitudinal section prove? What is Bhown by 
tran- What is said <>t' the limbs 1 

1 .". Describe the layers of the skin. 

K. EJow -I-- - the -kin differ from mucous membrane? 

1 7. What i- connective tissue ? 

: 8. What i- said of the muscles } 

l'.«. stitutes the skeleton? How many bones does it con- 
tain ? How are they fastened together? 

20. What enables ns to Btand apright ? 

21. What of the relation of the mind t<» the muscles f 

ins control the action- <»f the muscles 1 What special 
pmal axis posw 
What i- d -|»« cial -• asatt ime the organs which 

rfain kind- of imprt What are the] called? 

What i- ->ai'l ot the renewal of 



454 QUESTIONS. 

25. What are the organs of alimentation ? 

26. Name the organs of distribution ? 

2V. What is meant by the exchanges of the blood ? 

28. Name the principal excretory organs. In what respects do they 
resemble each other ? 

29. What important additional purpose do the lungs fulfill? 

30. What part does the nervous system plav ? 

31. What is meant by "life" and*" death ?" 

32. What is "local death? " 

33. What is "general death ? " 

34. How does death result ? 

35. What becomes of the body after death ? What forms mav its 
matter subsequently take ? 



CHAPTER II. 

36. Describe the capillaries. What is their function ? How are they 
distributed ? 

37. Of what are the capillaries continuations ? How do they differ 
from the small arteries and veins ? 

38. How are the muscles of the small arteries disposed ? 

39. What does their contraction effect? 

40. How is their contraction regulated ? 

41. Wherein do the arteries and veins differ ? 

42. Describe the valves of the veins. How may their action be de- 
monstrated ? What arteries possess valves ? 

43. Describe the lymphatics. Where are they distributed ? Where 
do they discharge their contents ? 

44. What are the lacteals ? What is their function ? 

45. What large trunks pour venous blood into the heart ? From 
what great trunk do most of the arteries spring ? What vessels carry 
blood to and from the lungs ? Into what parts of the heart do these 
various trunks open ? 

46. What vessels supply the substance of the heart ? 

47. What great vessel carries venous blood from the abdominal vis- 
cera to the liver ? What vessels conduct the blood from the liver to the 
heart ? 

48. What is the average size of the heart ? What its shape and posi- 
tion ? By what membrane is it inclosed ? 

49. Describe the cavities of the heart ? What are they called ? 

50. What is their relative amount of work? 

51. What tissue makes up the walls of the heart ? What membrane 
lines the cavities of the heart ? How are the communicating apertures 
strengthened ? What are attached to these rings ? 

52. Describe the structure and attachments of the heart-valves. What 
valves close the right auriculo-ventricular aperture? What the left? 
How are the free edges of the valves supported ? What is the action of 
these valves ? What valves are situated at the commencement of the 
aorta and pulmonary artery ? What is their action ? How may the ac- 
tion of the valves be demonstrated ? 

53. What is said of the rhythm of the heart ? What is meant by 
" systole " and " diastole ? " 



QUESTIONS. 455 

54. Describe the working of the heart. 

55. What is the action of the arteries ? 

56. What constitutes the beat of the heart ? 

57. What is said o( the sounds of the heart ? 

58. What constitutes the pulse ? 

59. Why does the blood jet from cut arter 
SO. Why are the capillaries pulseless ? 

61. What causes the steady capillary flow ? 

62. What is said of the velocity oi' the blood-current ? 

63. Trace the course of the blood from the i i^ht auricle. How is the 
heart itself supplied ? 

64. What is the shortest complete circuit the blood can make? The 
longest S 

65. How does the nervous system affect the circulation ? 

66. What happens in blushing ? 

67. How may this be proved ? 

68. What relation has this nervous control to disease ? 

69. What relation does the heart bear to the nervous system ? 

70. How may the movements of the heart be directly observed ? 

71. What is the proof that the blood circulates ? 



CHAPTER III. 

7_. How may we obtain blood for examination ? 

73. How does it appear to the naked eye ? How under the pocket- 
lens ? What takes place when a drop is left to itself? What is the ef- 
fect of salt upon it ? 

74. How many kinds of corpuscles does the blood contain ? 
7"). Describe them. 

7»>. What is the structure of the red corpuscles ? 
77. What are the peculiarities of the white corpuscl 
7v How may the real nature of the corpuscles be determined '? 
7' ( . What is supposed to be their origin ? What is said of the cor- 
puscles of the lower animal- ? 

Sl >. What occur- to the corpuscles when the blood di 

81. How are blood-crystals formed ? 

B2 What i- meant by coagulation? 

83. Into what coDstituentfl does the blood separate? 

B4. What is t *t ? 

85. What con litions influence coagulation ? 

86. What is the nature of the process ? What causes the blood to 
coagui 

87. Name some of tie- physical properties of the blood. 

88. What is its chemical composition '? 

89. Sow do « ;i'_ r <' influence the blood : Pood J 

90. What i- th.- total amoonl in the body? 

91. What i- tie- function of the blood? To what does it owe its vivi- 
inflaence ? What i- -aid of the transfusion of blood J 

What of th<- lymph f 



456 QUESTIONS. 



CHAPTER IT. 

93. What gives the blood its complex composition ? 

94. How is the blood changed in the capillaries ? 

95. In what respects do arterial and venous blood differ ? 

96. What is said of the diffusion of gases ? 

97. Why does the blood change color? 

98. How is this change explained ? 

99. Describe the capillaries of the lungs. 

100. Trace the air-passages from the mouth to the air-cells. 

101. What is said of this mechanism ? 

102. What are inspiration and expiration ? 

103. State the difference between inspired and expired air. 

104. What quantity of air passes through the lungs in twenty-four 
hours ? To what extent is it vitiated ? How much carbon and water is 
eliminated in twenty-four hours ? 

105. What mechanism carries on the respiratory movements ? What 
is said of the elasticity of the lungs ? 

106. How do the bronchial tubes facilitate the movement of air ? 

107. Describe the action of the chest-walls. Explain the action of 
the intercostal muscles. 

108. What is the diaphragm ? Explain its action. 

109. What occurs when the diaphragm acts alone? What if only 
the chest-walls are brought into play ? 

110. What other muscles aid the process ? 

111. How does the respiration differ in the sexes ? 

112. What is meant by residual air ? Supplemental air? Tidal air ? 

113. What constitutes the stationary air? What part does it play in 
respiration ? 

114. What is the composition of the stationary air? 

115. How is the nervous system related to respiration ? 

116. In what are respiration and circulation analogous ? 

117. What are the secondary phenomena of respiration? 

118. What is said of the respiratory murmurs? 

119. How does respiration assist the circulation ? 

120. What are the facts relating to this point ? 

121. How does expiration affect the circulation ? 

122. How may the action of the heart be arrested ? 

123. What circumstances modify the respiratory function? 

1 24. What occurs when a man is strangled ? 

125. How is life destroyed by this means ? 

126. What is said of respiratory poisons ? 

127. What is slow asphyxiation? 

3 28. Why is ventilation so important ? 



CHAPTER V. 

129. Describe the distribution of arterial blood throughout the body. 

130. What great organs are constantly draining the blood ? 

131. What is said of its losses in the liver and lungs ? 

132. What are the intermittent sources of loss and gain to the blood ? 



QUESTIONS. 45 7 

133. What are the incessantly active and intermittently active Bources 
of loss and gain to the blood ! 

184. Give the position and anatomy of the kidneys. 

185. What is the composition of the renal excretion? What is its 
average daily amount } lt< average specific gravity ? 

186. In what respects are the lungs and kidneys alike? 

187. Describe the Btructnre of the kidney. 

188. What is said of its filtering mechanism ? 

lo'.». From what BOUIce are the kidneys BUpplied with blood? How 

do they change the blood? 

140. How is the excretory action ot the kidneys controlled? 

141. What does the Mood lose through the skin ? 

142. Whal quantity of matter is thus lost ? What is the composition 
of the sweat ? 

143. Give the conditions of its escape. 

144. What is said of the Bweat-glands ? What of their distribution V 

146. How is the action of the sweat-glands controlled ? 
lit). What conditions increase the amount of perspiration ? 

147. Hi what respects are the lungs, kidneys, and skin alike? 

148. What does the blood lose in the liver? What does it pain ? 
Describe the liver. With what great ves>els is it connected? Give its 
internal anatomy. What route does the blood take in its passage through 
the liver? What is said of the liver-cells? 

149. What i> their function ? 

150. What i- the daily quantity of bile exereted ? Its composition ? 
l"»i What is the source.ol the bile? 

* 152. What organs furnish the blood with oxygen ? 

153. What does the blood gain in the liver? What does it lose? 

154. How may the BUgar-forming power of the liver be proved ? 

155. What does the blood gain from the lymphatics? What of the 

ls ductless glands ? " 

156. What i- said of the spleen ? What is its Bupposed function? 

157. Through what channels does the body lose heat ? What is the 

source of bodily heat ? 

158. Bow is the heat of the body equalized ? 

159. How does evaporation affect the temperature ? 

150. What relation has the nervous Bystem to temperature? 

161. Wh.it is -aid of the action of tie- glands? What is the duet of 

a gland? What are racemose glands ? What determines the activity 

' tain glands ? 
1 62. In what way are the Balivary glands called into action ? What 

is the character of their Becretion ? 

168. What doc- the blood gain from the muscl - 



CHAPTEB VI. 

164. What i- another great source of gain to the blood? 

165. How much -olid mateiial doc- a man daily reeei\r ? HOW tDUeh 

166. What is the daily lost of dry BOlidft ? In what shape does the 

balance leave tin- body F 

L69 ssified! What are Proteids ? Give examples. 



456 QUESTIONS. 

What is the composition of fat ? What are Amyloids ? Give some ex- 
amples. What is meant by " vital food-stuffs ? " What are mineral 
food-stuffs ? 

168. What is the composition of the vital food-stuffs ? The mineral 
food-stuffs ? What constitutes a permanent food ? 

169. What occurs if protein is not supplied? What is said of the 
necessity of other food-stuffs ? 

170. What is meant by nitrogen starvation ? 

171. 172. What are the disadvantages of a purely nitrogenous diet ? 

173. Why is a mixed diet desirable? 

174. What constitutes a mixed diet ? 

175. What is said of the intermediate changes of the food ? 

176. What are the objections to the ordinary classifications of food? 

177. What is the purpose of the alimentary apparatus ? 

178. Describe the cavity of the mouth and pharynx. What organs 
do they contain ? Name the openings into the pharynx. 

179. Give the names and positions of the different salivary glands. 
How does the saliva affect the food ? 

180. Describe the teeth. 

181. Describe the working of the jaws. 

182. What occurs to the food during mastication? Describe the 
operation of swallowing ? 

1 83. How are fluids swallowed ? 

184. Describe the stomach. What is the character of its lining mem- 
brane ? What glands does it contain ? What fluids do these glands 
pour out ? What are the properties of the gastric juice ? 

185. What is meant by artificial digestion? 

186. Describe the process of osmosis. 

187. By what routes does the food leave the stomach ? 

188. What is said of the intestines? How are they divided? Where 
is the ileo-caecal valve situated ? What is the caecum ? The vermiform 
appendix ? 

189. What glands are found in the intestinal mucous membrane? 
What other structures ? 

190. What is peristaltic contraction ? 

191. What glands pour their secretions into the duodenum? What 
is said of the chyme ? 

192. What is chyle? How does it differ from chyme ? What changes 
does the chyme undergo in the intestine ? What juices effect this change ? 
In what way does the chyle reach the blood ? 

193. What is going on in the large intestine ? 



CHAPTER VII. 

194. What is meant by the "vital eddy ? " What maintains the ac- 
tive powers of the body ? 

195. In what way are the activities of the body manifested? What 
is locomotion ? Name the organs of motion. 

196. Describe the cilia. How do they act? Where are they situated? 

197. How do the muscles give rise to motion? Into what two groups 
may the muscles be divided ? 

198. What is rigor mortis ? 



QUESTIONS. 459 

199. What is the chemical composition of muscle? 

200, 201. What muscles arc not attached to solid levers? What is 
the character of their fibres ? What is said of their contractions ? 

'202. What muscles are attached to solid levers ? What is a lever? 
203. How many orders of levers are described? What is a lever of 
the tirst order ? Of the second order ? 01' the third order ? 

2<U. What levers of the first order are found in the human body? 

205. What of the second order? 

206. What of the third order? 

207. How may a single part of the body represent the three kinds of 
levers ? 

208. How many kinds of joints are found in the human body? 

209. What are imperfect joints ? 

210. Describe the structure and movements of a perfect joint ? 

211. What are inter-articular cartilages? 

212. What are ball-and-socket joints ? 

213. What are hinge-joints? 

214. What is a pivot-joint ? Give an example from the human body. 
Describe the bones of the forearm. How are they articulated together ? 
What is meant by pronation and supination? 

215. What are ligaments? How do the ligaments differ in the dif- 
ferent joints ? What is said of the hip-joints ? 

216. What different movements are the joints capable of executing? 

217. How are these movements effected? In what way are they 
limited ? 

2 IS. What is meant by .the origin and insertion of a muscle? How 
are the muscles attached to the bones ? What direction does the axis 
of a muscle usually take ? The exceptions ? 

210. Describe the operation of walking. 

220. When does a man walk with least effort ? 

221. What is said of running and jumping ? 

What conditions are essential to the production of voice ? 

223. Describe the vocal chord- ? 

224. What cartilages enter into the structure of the larynx ? 
To what are the vocal ligament- attached ? 

I 1 scribe the muscles of the larynx. What does their actiou ef- 
fect ? Dow are musical notes produced ? 

227. When will the musical note be low ? When high? Upon what 
range Ol voice depend? Upon what the quality of voice? 

228. What is Bpeech? How is the voice modulated? 

229. What is said of the vowel sounds? What of consonant sounds? 
What sounds require blocking of the air-current ? What are explosive 
consonants ? 

BOW are Speaking-machines constructed ? 

281. What is -aid of tonguelesfl speech? What example is given? 



CHAFTEB Vlll. 

2.°/_\ How arc the muscles made to contract ? 

What call- the Dei v< s into action ? 

What ifl reflei sction ? What u a sensation } With what are 
laased ? 



460 QUESTIONS. 

235. What are subjective sensations ? 

236. What is said of the muscular sense ? How may its existence 
be demonstrated ? 

237. What is said of the higher senses ? 

238. Give the general plan of a sensory organ. 

239. Where is the organ of the sense of touch located ? What are 
papillae ? What is a tactile corpuscle ? 

240. What is interposed between it and external objects ? 

241. What is said of varying tactile sensibility ? 

242. What gives rise to the feelings of warmth and cold ? 

243. Where is the organ of the sense of taste found ? Describe the 
papillae of the tongue. 

244. Where is the organ of the sense of smell located ? Describe the 
nasal passages. The nasal chambers. What do these nasal chambers 
contain ? 

245. How are odors brought in contact with the olfactory apparatus ? 

246. Where is the organ of hearing situated ? Of what does it essen- 
tially consist ? What bodies are found in the membranous labyrinth ? 
In the scala media ? 

247. What part of the ear is called the vestibule ? What are the 
semicircular canals ? What the ampullae ? What fluids form a part of 
the mechanism ? 

248. Where is the scala media situated ? What part is known as the 
scala tympani? The scala vestibulif What peculiar mechanism is found 
within the scala media f 

249. What is the bony labyrinth ? What fenestra? docs it contain ? 

250. What part of the ear is known a> the drum 9 How is this sep- 
arated from the external meatus? In what way does the drum commu- 
nicate externally ? 

251. What are the auditory ossicles? What two points do they con- 
nect ? What is their purpose ? How are the perilymph and endolymph 
set vibrating ? 

252. What muscles are connected with the tympanic membrane ? 

253. What is the concha ? 

254. What conditions are necessary to the production of sound ? 
How is sound transmitted to the ear ? 

255. How do the aerial vibrations affect the tympanic membrane ? 
Into what two kinds of vibrations may bodies be thrown ? 

256. Which are supposed to transmit the impulses of the aerial 
waves ? 

257. Describe the actions of the auditory muscles. 

258. What part of the ear is supposed "to recognize the intensity of 
sounds ? What part is concerned with the quality of sounds ? 

259. What is the probable function of the fibres of Corti ? 

260. What is the purpose of the Eustachian tubes ? 

CHAPTER IX. 

261. Describe the general structure of the eye. 

262. What is seen on the centre of the retina ? 

263. Describe the microscopic structure of the retina. 

264. What is the function of the retina ? What is said of the sen- 
sation of light ? 






QUESTIONS. 461 

265. In what respects do different parts of the retina differ ? What 
is the blind spot ? 

266. What is Baid of the duration of luminous impressions ? 

207. Can the retina become exhausted ? What are complementary 
colors ? 

268. What is color blindness '- 

What appearances are produced by pressure upon the eyeball ': 

•27". What is the function of the rods and cones ? What are Pur- 
hinje'sfigv 

271. What is said of the formation of visual ideal 

•27-. What physical agent gives rise to vision ? What i- a convex 
lens ? Describe the experiment with the candle and lens. 

'273. What is meant by the " focus ? n What is adjustment of the 
eye? When does the lens give a distant picture? What is the effect 
of moving the object ! 

274. What follows from Varying the convexity of the lens ? What 
relation docs convexity bear to the focus ? How does a convex surface 
affect the rays of light ? Describe the experiment with the watch-glass 
and water-box. What is a camera obscure ? 

27-">. What organs must the light pass through to reach the retina ? 
Give the structure of the eyeball. 

What are the humors of the eye ? By what organ are the 
humors separated ? Describe the crystalline lens. 

277. Describe the choroid coat. What is its position ? Where are 
the ciliary processes situated ? 

278. Describe the iris. Where is it situated? What of the ciliary 
muscle ? What relation has the iris to the lens ? 

'. What is the ora -errata ? 

is the eyeball resemble a water-camera ? 

281. How is the focus adjusted in a camera obecura? How in the 

282. Describe the experiment. What does it show? 

What is said of the mechanism of adjustment ? What arc the 
a of adjustment? What explanations of the process have been of- 
fered ? Which is the most probable ? 

28 1 What limits the power of adjustment ? 

285. Name tic muscles of the eyeball. What are their respective 

positions ! What does Their action effect ? 

scribe the .-tincture of the eyelids? What muscles move 

287. Where is the conjunctiva -ituated ? Describe the lachrymal ap- 
paratus ? What i> tic source of the tears ? 



CHAPTER X. 
meant by a simple sensation \ What is the character 

of I J i « » - T Of • 

tie- simplest \ 
>. Of what '1<H- ;i tactile Bensation consist? 
•-".♦l. Wl afcomplei sensations and judgments ? 

nset impossible ! What is -aid of 

delu-i UtS? 



462 QUESTIONS. 

293. What are subjective sensations ? What examples are given ? 

294. Relate the case of Mrs. A . What senses were implicated ? 

To what class did her peculiar sensations belong ? 

295. What conditions seemed to favor their development ? What 
prevented her forming false judgments ? 

296. Were her senses really at fault ? 

297. How may outside causes give rise to delusive judgments ? Give 
an example. 

298. What is said of optical delusions ? 

299. What is meant by the optic axis ? How is the position of a 
phosphene accounted for ? 

300. What is said of the inversion of visual images ? 

301. How do objects and their visual images correspond in number ? 
What is the action of multiplying-glasses ? 

302. Upon what does perspective depend ? 

303. How does the distance of an object affect its visual image? 
How do convex and concave glasses affect it ? 

304. Why do the sun and moon look larger near the horizon ? 

305. What is said of the judgment of form by shadows ? 

306. What is the principle of the thaumatrope ? 

307. What is the explanation of squinting ? 

308. Give the principle of the pseudoscope. 

309. What of the stereoscope ? 



CHAPTER XL 

310. Of what is the bulk of the nervous system made up ? 

311. What two systems constitute the nervous apparatus? 

312. Describe the structure of nerve-fibres and nerve-centres. 

313. Where is the cerebrospinal axis located ? What membrane 
separates it from the bone ? What other membranes surround the brain 
and cord ? 

314. Describe the spinal cord. How is it divided? Describe the 
roots of the spinal nerves. 

315. What does a transverse section of the cord show ? 

316. How do gray and white matter differ ? 

317. What follows the irritation of a spinal nerve ? 

318. What are the functions of the anterior and posterior roots ? 

319. What results from cutting the anterior root of a spinal nerve? 
The posterior root ? Both roots ? 

320. How are impressions propagated along the nerves ? What is an 
afferent nerve ? What is an efferent nerve ? 

321. In what respects are they alike ? 

322. What occurs when the spinal cord is cut across ? What when 
the end remote from the brain is irritated ? 

323. What power does the cord possess independently of the brain ? 

324. What is said of the distribution of reflex effects ? 

325. Do all parts of the cord possess a like conducting power ? 

326. What is said of the conducting power of the gray matter? 

327. What special functions have certain regions of the cord ? 

328. Describe the medulla oblongata. What cavity does it contain ? 
What overhangs this cavity ? What is the pons Varolii ? Into what 



QUESTIONS. 463 

parts do the fibres of the medulla pass? What elevations are found be- 
tween the crura cerebri? Where is the third ventricle situated? Into 
what masses of nervous matter do the crura cerebri pass ? Where is the 
pineal cjl'Did located 9 The pituitary body ' Where are the lateral ven- 
a situated ': What tonus the floor of the lateral ventrieles ? What 
id of the hemispheres of the brain \ How are they connected ? 
What is Baid of the outer surfaces of the hemispheres \ 

How are the white and gray matter arranged in the medulla ob- 
longata ': In the cerebellum and cerebral hemispheres? 

How many pairs of nerves are given oil from the brain? Name 
the first pair. The second. The third. In what muscles is the third 
pair distributed ? Where are the fourth, and sixth pairs distributed ? 
vibe the origin and distribution o^ the fifth pair. In what muscles 
- enth pair terminate:-' The eighth pair terminate ? What 
is the function of the ninth pair? What organs does the tenth pair sup- 
ply? Describe the course of the eleventh pair. Give the origin and dis- 
tribution of the twelfth pair. 

SSI. What is said of the olfactory and optie neives ? 

332. What effects follow injuries of the medulla oblongata ? 

What direction do the afferent impulses take in the medulla ob- 
longata ? (live the course of the fibres in the anterior pyramids. What 
would be the effect of dividing one of the crura cerebri ? 

1. What is the function of the cerebral hemispheres? 
". What is said of the reflex action of the brain ? 
336. What takes place in reading aloud ? 

7. What is meant by "artificial reflex actions ? M 
What is said of the sympathetic tyttem ' 



CHAPTER XII. 

What i- Baid of the microscopical analysis of the tissues? 
. What is the early primitive structure of the body ? 
541. What is the character of the epidermis and epitheUum / How 
do these I 3G ow? What is tqvanunu epithelium J What kind of 

epithelium lines the alimentary canal ? What is ciliated epithelium? 
'■_'. From what kind of tissue are the nail- developed? 

of what are hairs composed ? Describe their growth. How are 
the hairs kepi supplied with oil'/ What i.- meant by horripilation, or 
- -skin ? "' 
:.! i. What is the structure of the crystalline lens? 

545. Of what is cartilage composed ? 

546. Whal is the structure of eonneefi How is it affected 
by being boiled in water? I acetic acid affect it? What is 

ent-celle ? 
D scribe the minute structure of bone Whal are lacuna 9 
e the lacunae once supposed to be? Describe 
the Ham da. What what is found in the 

cavities of the 

Hoi do bones (troa ? Wh In what kind of 



464 QUESTIONS. 

material are bony matters first deposited ? What is meant by centres of 
ossification ? 

352. Of what are the teeth composed ? Name the different parts of 
a tooth. What is the character of dentine ? What is the structure of 
enamel ? 

353. How are the teeth developed ? Which are the deciduous, or 
milk-teeth ? When do they appear ? 

354. How are the permanent teeth formed? How divided? When 
do they begin to appear? How long before the set is completed ? 

355. What two kinds of muscles are found in the body ? Of what 
are the striated composed? What is & fascia? The sarcolemma? 
What does it inclose ? Of what is the contractile substance made up ? 
W^hat is the structure of smooth muscle ? 

356. What are the elements of nerve-tissue ? Describe the structure 
of a nerve -fibre. How do the nerve-fibres terminate ? 

357. What is a tactile corpuscle? 

358. What is the structure of the olfactory nerves ? 

359. Where are ganglionic corpuscles found ? What is their struct- 
ure ? 

CHAPTER XIII. 

360. Give the weight of the different parts of the body. How much 
of the body is water ? How much solid matter ? What do the solids 
consist of ? What would be the losses of such a bady in twenty-four 
hours ? Through what organs would these losses occur ? How much 
does the body gain in twenty-four hours ? 

361. What substances, and how much of each, dees the body daily 
require ? In what forms could these be conveniently obtained V 

362. How much blood passes through the heart per minute? At 
what rate does it flow in the large arteries ? In the capillaries ? What 
is the daily work of the left ventricle ? 

363. How much air passes through the lungs in twenty-four hours ? 
How is it changed in the passage ? What does the body lose by respira- 
tion in twenty-four hours ? At what rate does the respiration of a sin- 
gle person vitiate the external air ? 

364. How much matter is lost through the skin in twenty -four 
hours ? 

365. How much by the kidneys ? 

366. What is the velocity of a nervous impulse ? 

367. W r hat is the size of the blood-corpuscles in man ? AVhat the 
thickness of his muscular fibres ? What the breadth of nerve-fibres ? Of 
connective-tissue fibrils? Of epithelium - scales ? Of capillary blood- 
vessels ? Of the cones in the yellow spot ? How long are the cilia of 
the windpipe ? 



QUESTION- 465 



F>.Yrc T S ECOND. 



CHAPTER XIV. 

568. Of what practical value is a knowledge of physiology ? What 
is said of its importance ? 

■ What were Borne ofthe old notions regarding disease ''. How did 

such views affect the community ? 

What is the true idea of health ami disease \ Bow is this illus- 
trated in the ease of gout ? 

371. When do the agencies of health become sources of disease! 
What is the chief value of hygienic knowledg 

37*2. Name some ofthe results that have followed its application \ 

373. What i- said of its value as a remedial mean.- \ 

374. What are the chief sources of ill health ? 



CHAPTER XV. 

375. Name the chief constituents ofthe atmosphere ? 
. What are its minor constituent- ? 

What is the office ofthe air in respiration ? 
-. What i- Baid <»t 'ir as a purifying agent \ 
How i- the air rendered impure ? 
380. How do atmospheric impurities affect the sex 

What is said of carbonic acid as an impurity ? In what propor- 
tion is it thrown out from the Longs ? From what other sources does the 
air of apartmeir- :r ? What does an excess of it denote ? 

382. What is the effect of air saturated with moisture? Of dry air? 

383. In what form is organic matter found in th«' airy What are 
some of i :- By what means may we determine it- presence? 
SVh in the air of sick-rooms and hospitals \ How 

• affect U 

led impurities are common in the air? 
Qter it firoi - rod cessp 

386. What contamination- are found in the air of marshes \ 

\ the air ol cell 
388. W .1 effect upon the body of impure air*? 

380. What is said of impure air and consumption ? 

t ha- impure air upon the scrofulous ! Eft late the 
case of the Norwood - 

urinated by certain trades affect the health? 
of inhaling air containing organic impurities? 
drafted the course of disease ? What i- of 
the fn -■ ' febrile complaints ? 

i sick-room atmospl 
oi impure air upon the mind ? 
>urifj th< 

Dtilatum! How iiiuv pure air be best 



466 QUESTIONS. 

obtained ? What quantity of air is required ? How may its movement 
be controlled ? What is said concerning its temperature ? 

398. When are other means of purification required ? What sub- 
stances are most efficient a,s disinfectants ? 

CHAPTER XVI. 

399. What proportion of water do the various tissues contain ? 

400. What duties does it perform in the economy ? 

401. What leading property fits it for this office? 

402. The average daily consumption of an adult ? 

403. What is said of its excretion ? 

404. What gives rise to the several varieties of water ? 

405. What is said of soft water ? 

406. How is hard water formed ? What are mineral waters ? Give 
the characters of limestone-water. What is said of sand and gravel 
waters ? What are the foreign ingredients of alluvial waters ? The im- 
purities of surface and subsoil waters ? What is said of marsh-water ? 
What is the general character of river-water ? What is said of sea- 
water ? 

407. How may perfectly pure water be obtained? What water may 
be regarded as most healthy ? 

408. What is said of the organic impurities of water ? 

409. How is water affected by contact with lead ? 

410. What kinds of impurities are likely to produce dyspepsia ? 

411. What kinds of water are said to produce diarrhoea? 

412. 413. Are dysentery and cholera ever caused by impure water? 

414. What is said of the spread of enteric fever ? 

415. How are malarious fevers often produced ? 
418. What is the supposed cause of goitre ? 

417. What animals may pass into the body with the drinking-water ? 

418. Are the senses alone trustworthy in the examination of water ? 

419. What is said of distillation as a means of purification ? 

420. What is the effect of boiling and freezing ? 

421. What chemical substances are sometimes used as purifiers ? 

422. What is said of filtration ? 



CHAPTER XVII. 

423. Into what four groups may food be classed ? 

424. What is said of the proteids ? 

425. What of the fats as articles of diet ? 

426. What substances belong to the amyloid group ? 

427. To what uses are these various food-stuffs applied ? 

428. What are the mineral aliments? 

429. Why is a mixed diet necessary ? 

430. What is said of milk as food ? 

431. Of butter and cheese? 

432. What is the composition of eggs, and how should they be 
cooked ? 

433. What is said of the various meats ? 

434. Why is salt inferior to fresh meat ? 









QUESTIONS. 467 

435. What peculiarity do poultry and game present? 

436. How is the flesh of fish regarded as food V 

437. 438, What is said of crabs and lobsters ? Clams and oysters? 

439. Why is wheat such a valuable food ? 

440. How does rye compare with wheat? 

441. What of buckwheat ? 

442. How does Indian corn differ from wheat and rye . J 

443. What are the properties of oatmeal ? 

444. What advantage does rice possess over other foods ? 
44.">. What is said of peas and beans ? 

446. Give the composition of potatoes. Why should the succulent 
tables be eaten with meat ? 
' 447. What is said of the fruits * 
148. What are auxiliary foodfl ? 
449. What substances come under the head of condiments ? 

460. Why is tea valuable as a beverage? How should it be made? 
What is its action ? How is it adulterated ? 

451. What is the composition of coffee ? How should the beverage 
be prepared ? 

452. What is said of cocoa and chocolate? 

453. What should cooking aim to accomplish ? Why should over- 
cooking be avoided ? 

454. How does boiling affect meat ? How should the process be con- 

What is said of roasting ? Stewing? Frying? 

455. How should vegetable- bo eooked ? 

456. What are some of the effects of over-eating ? 

457. What are the effects of deficient diet ? 
158. What amount of food is daily required? 
459. What results from a badly-constituted diet? 

. What is -aid of a diet deficient in fat : 

461. What constitutes unwholesome food ? 

462. dive an account of the cysticercus cellulosus. Of the trichina 
spiralis. 

CHAPTEB XVIII. 

What i- said of the purposes for which clothing i< worn ? 
1. What ot linen a- an article of clothing? 
465. How does cotton differ from linen? 

What aie the properties of woolen clothing? Its relations to 

167. How does color influence the character of clothing? 

468. What is of more importance than the character of the fabric f 

169. Why Bhould clothing be light ? 

1 7 ■'. Why Bhould it be worn loos 

471. W h o is said of compressing the chest and abdomen ! 

172. w -in ■_-■ the feel ? 

How i- uniformity of temperature t<> !»«• maintained! 
J7J. How i- a part when habitually overheated ? Why is 

jsing the tfrroat perniciouf 
175. Wh ^ fa g ,i i of (rearing flannel next the -kin F 

ild children be clothed v 
177. Why should U protects 



468 QUESTIONS. 



CHAPTER XIX. 

478. What renders it evident that man is intended for action ? 

479. What is said of labor ? What causes division of labor? How 
does it affect the individual ? 

480. How does exercise remedy the evil ? 

481. Describe the transformation of physiological forces. 

482. Why is habitual exercise invigorating ? 

483. How does exercise affect the circulation ? How the tempera- 
ture? 

484. What is its influence upon respiration ? Why should we exer- 
cise in pure air ? 

485. How does exercise affect digestion ? Why is immediate exer- 
cise after a full meal injurious ? 

486. Whit is the effect of exercise upon the skin ? 

487. How should exercise be regulated ? 

488. W x hat are the most favorable conditions for exercise ? 

489. Why is' over - exercise injurious? How is proper rest to be 
secured ? How should exercise be managed after sickness ? How does 
over-exercise injure the system ? Why does it particularly injure the 
young ? 

490. What are the consequences of insufficient exercise ? Describe 
its operation in different circumstances. 

491. What is said of the amount and conditions of exercise? What 
course should the sedentary pursue ? Why is pure air specially neces- 
sary during exercise? 

492. What is the value of the " movement-cure ? " 



CHAPTER XX. 

493. Why is mental health a physiological question ? 

494. What is said of the office and changes of the brain ? What is 
the effect of disturbing its normal movement ? Describe the mutual re- 
lations of the mind and brain. What is remarked as to materialism ? 

495. What constitutes disease? What error is to be guarded against? 
How is mental disease to be regarded ? On what is mental hygiene 
founded ? What is its province ? 

496. Why are the causes of cerebral impairment varied and com- 
plex ? How are they usually divided ? What are predisposing causes ? 
Exciting causes ? What error is mentioned ? In what way is insanity 
usually caused ? 

497. What is said of each mental act ? What are the composition 
and action of the mental mechanism ? What are the results of its per- 
fect or imperfect nutrition ? Repeat the remarks of Bucknill and Tuke. 
What further effect is due to impaired nutrition ? 

498. What is said of the blood transmitted to the brain? 

499. What are the relations between mental excitement and the 
brainward flow of blood ? How is congestion induced, and what are its 
effects ? * 

500. What is anaemia, and how caused ? What are its effects as 
compared with those of hyperemia ? Give Dr. Maudsley's remarks upon 
the subject. 



QUESTIONS. 409 

501. What keeps the brain in harmonious action ? How may its 
harmony be farther disturbed ? Mention examples of perversion of 
blood. How does alcohol affect the brain ? 

602. How dees the brain differ in action from other organs of the 
body ? How does Nature renovate the brain V What i- a prime condi- 
tion of mental health ? What are the effects of insufficient sleep ? What 
of disturbed sleep? In what does mental health consist? From what 
arises mental impairment? Bence, what causes influence mental char- 
acter ? 

Give the estimates relative to the transmission of insanity. What 
i- transmitted, and how ? Repeat the remarks of Dr. Maudslex. 

504. lb>w is debilitated stock a Bource of criminality ? What is Dr. 
Howe's opinion upon this Bubject ! Name some of the causes of mental 
impairment and their operation. Give the observations of Dr. Kay. 

505. What comparison is made, between the savage and the civilized 
man ? What are our peculiar perils as a nation ? 

506. What i> said of overtasking the intellect? Repeat the testi- 
mony of Dr. Carpenter. What conditions control the amount of health- 
ful brain-work ? How is the argument against the unwholesome effect 
ot excessive brain-work met ? In what respect does the brain of the 
savage and the civilized man differ? What usually works the mischief 
in cerebral application ? 

How is cerebral disease heralded ? How the more active forms? 
In what manner is the conduct affected? The consciousness ? 

508. What hints and precautions are given ? How should children 
thus predisposed be managed ? How adults ? What is Dr. Ray's advice 
\shen there i< a predisposition to mental disease P 

5<»v. What is said of medical management ! 



INDEX AND GLOSSARY. 



[iV. B. — The figures refer to paragraphs.] 



Abdo'men, the belly, 10. 

Abdominal aorta, 129. 

Abduction, that movement by which 
one part is drawn away from an- 
other, or from the middle line of 
the body, 216. 

Absorption, the sucking up of sub- 
stances applied to the mouths of 
absorbent vessels, 187, 192. 

Accessory food-stuffs, 17&. 

Acetabulum, the round cavity in 
the haunch-bone which receives 
the head of th$ thigh-bone, 215. 

Acidulous waters, 405. 

Action, man intended for, 478. 
" of the valves of the veins, 
42. 
" of the valves of the heart, 
52. 

Active powers, 195. 

Adam's apple, 224. 

Adduction, that movement by which 
one part is drawn toward another 
or toward the middle line of the 
body, 216. 

Adjustment of the eye, changes in 
that organ by which objects at 
varying distances are distinctly 
seen, 280, 285. 

Adulteration of coffee, 451. 
" of milk, 430. 

11 of tea, 450. 

u of vinegar, 449. 

Aerial waves, 254. 



Afferent nerves, nerves which, un- 
der the influence of impressions 
from without, excite the central 
nervous organ, 232. 
Agencies of purification, 378, 396- 

398, 418. 
Air-cells, 100. 
Air, complemental, 112. 
" composition of, 103, 475. 
" contamination of, 379-387. 
" danger of overheating, 397. 
" inspired and expired, \^o. 
" in respiration, 112, 3(33. 
" residual, supplemental, and tid- 
al, 112, 
Albu'men, a nitrogenous substance 
extensively diffused in the animal 
and vegetable kingdoms, and co- 
agulable by heat — white of egg, 
167. 
Alcohol, effects of, 451, 
Alimentary apparatus, 25. 

" canal, 12, 132, 164. 

Alimentation, the act of taking or 

receiving nourishment, 24. 
Aliments, food-stuffs, 167. 

" classification of, 167. 
Alluvial waters, 405. 
Al'veoli, the sockets of the teeth, 

180. 
Ammonia, 28, 376. 
Amce'ba, one of the lowest of ani- 
mal organisms, 78. 
Amphibia, blood-corpuscles of, 79. 



INDEX AND GLOSSARY. 



471 



Ampul'la?, the trumpet - mouthed 
parts of the Bemicircular canals 

of the ear, 247. 

Amyloids, a class of food-stuffs, 
of which starch is the type, 
167. 

Anatomy, an account of the struct- 
ure of organized bodies. 1«>. 

Anaemia, deficiency of blood, 5<»n. 

Animal charcoal, 223. 
- foods, 43<»-438. 

Ankle-joint, 213. 

Antrum, cavity of the upper jaw- 
bone, 226. 

Anus, 190. 

Aorta, the great vessel which eon- 
ducts arterial blood from the 
heart, 45. 

Apex of the heart, 48. 

Applied physiology, 368. 

Arachnoid, resembling a spider's 
web, applied to a delicate, cob- 
web-like membrane which envel- 
ops the brain, 312. 

Arachnoid fluid, a serous fluid se- 
creted by the arachnoid .mem- 
brane, 312. 

Areolar tissue (see connective tis- 
sue), 17. 

Arms, bones of the, 19, 214. 

Arteria innominata, the first branch 
d off from the aorta, 48. 

Arterial blood, 95. 

" and veins, difference be- 
tween, 41. 
Artery, a v. --el which eonvevs 
blood outward from tin- la-art, 
37. 
Artery, hepatic, 148. 
" " renal, 137. 
" splenic, 156. 
Articulation*, joints, 
Artificial ona, 337. 

ling tli.' mouth 
of a pitcher, 22 l. 

Arvr js and muscles, 

224. 

spended animation ; 
usually e disturbance 

l -j 1. 
! . 1 •_' 5 
Atlas, the topi bra of the 



spinal column, with which the 

head is articulated, 214. 
Auditory muscles, muscles of the 

ear, 25 7. 

nerve, 246. 
ossicles, 251. 
spectra, 293. 
Auricle, right and left, the upper 

cavities of the heart, 49. 
Auriculo-ventricular openings, ring, 

and valves, 52. 
Auxiliary foods, 448. 
Axis, the second cervical vertebra, 
, on which the atlas turns, 214. 
Axis-cylinder, 356. 

Ball-and-socket joints, articulations 
where the spheroidal end of one 
bone plays in a cup-shaped cav- 
itv of another bone, 212. 

Base of the heart, 48. 

Beans and peas, 445. 

Beating of the heart, 55. 

Beef-tea, 454. 

Biceps muscle, 1§, 202. 

Bicuspid teeth, teeth with two cusps 
or elevated points on their wear- 
ing surface, 1 80. 

Bile, a greenish-yellow, viscid fluid 
secreted by the liver, 131, 148, 
150, 101. 

Biliary duct, 148. 

Bilin, a pale -yellow gummy sub- 
Btance, supposed to be the chief 
constituent of the bile, 15' ». 

Black clothes, 467. 

Black pepper, 449. 

Bladder, 134. 

Blind spot of the retina, point at 
which the optic nerve enters the 
eyeball, 265. 

Blood, appearance of, 72, 73. 
arterial and venous, 43. 
" " distribution of, 121). 

" changes of, 07 
11 circulation of, 26. 
" coagulation of, B2, 
composition of. 88. 
" corpuscles of, 7 1. 
11 crystals of; 81. 
" How of, through heart, 5 l. 
perversions of 889, 501. 
purification of. 99, '-77. 



472 



INDEX AND GLOSSARY. 



Blood, quantity of, in the body, 90, 

360. 
Blood, sources of loss and gain to, 

133. 
Blood, specific quantity of, 87. 

" temperature of, 157, 158. 
Blow on the head, effects of, 21. 
Blushing, 66. 
Body, structure and functions of 

the, 1. 
Boiling, 454, 455. 
Bones, 19. 

" structure of, 350. 

" their dissolution, 35, 

" of the ear, 256. 
Brain, 13, 22, 328, 335. 

" congestion of, 499. 

" nutritive repair of, 497. 
Bread, 174, 360, 361. 
Breast-bone, 19. 
Brewster, Sir David, 294. 
Broiling, 454. 
Bronchi, the first two branches of 

the windpipe, 100. 
Bronchial tubes, the minute ramifi- 
cations of the bronchi, terminat- 
ing in the air-cells, 100. 
Bronchitis, inflammation of the 

bronchi, 391. 
Brunner's glands, glands of the 

mucous membrane of the small 

intestines, 189. 
Buccal glands, glands in the mucous 

membrane of the cheek, 179. 
Buckwheat, 441. 
Buffy-coat of the blood, 84. 
Bursee, a sac or purse, 218. 
Butcher's meat, 433. 
Butter, 431. 

" of cocoa, 452. 

Caecum, the first portion of the 
large intestine, 1 88. 

Caffein, the bitter principle of coffee, 
451. 

Canalic'uli, narrow channels ramify- 
ing through bone, 350. 

Canals of the ear, 247. 

Cancellous tissue, applied to the tis- 
sue composing the loose, spongy 
portions of bones, 202. 

Canine-teeth, the eye-teeth, 180. 

Capillaries, minute vessels which 



.conduct the blood through the 

tissues, 26, 59, 61, 98. 
Capsular ligament, 215. 
Carbon, one of the elements — char- 
coal, 4, 167, 173, 361. 
Carbonate of lime, 3, 19. 
Carbonic acid, 3, 5, 28, 88, 95, 99, 

103, 123, 136, 163. 
Carbonic acid, poisonous nature of, 

125. 
Carbonic-oxide gas, 126. 
Carbonated waters, 406. 
Cardiac, pertaining to the heart, 184. 
Cardiac aperture of the stomach, 

184. 
Carotid arteries, 49. 
Carpus, the wrist, 214. 
Cartilage, 19, 32, 107, 208, 345. 
Caruncula lachrymalis, the reddish 

prominence in the inner corner 

of the eye, 287. 
Casein, the nitrogenized portion of 

milk, the curd, 167, 430, 431. 
Catherine-wheel, 266. 
Causes of disease, 370, 374. 
Cavities of the heart, 49. 
Cavity of the mouth, 178. 
Cayenne pepper, 448. 
Cellars, foul air in, 387. 
Cellular structure, 340. 
Cement of the teeth, the thin, bony 

coating of the fangs of the teeth, 

352. 
Central nervous organ, 232, 233. 
Cerebel'lum, the little brain situated 

in the lower and hinder portion 

of the skull, 328, 334. 
Cerebral hemispheres, functions of, 

334. 

" nerves, 329. 
" structure, nutrition of, 497. 
Cer'ebro-spinal axis, the brain and 

spinal cord, 13, 310. 
Cer'ebro-spinal axis, function of, 22. 

system, 311-318. 
Cerebration, unconscious, 334. 
Cer'ebrum, the larger division of the 

brain, occupying the whole upper 

portion of the cavity of the skull, 

328. 
Cervical, relating to the neck. 
Chalybeate waters, waters contain- 
ing iron, 406. 



INDEX AND GLOSSARY. 



473 



Changes of the food, 175. 
Charcoal as a deodorizer, 398. 

filters, 422. 
Chock ligaments, ligaments limiting 

rotation of the skull. 215. 
Cheeks, 242. 
se, 431. 
Chest, the cavity containing the 

hm^s and heart; the thorax, K). 
- ' hones of, 19, 
('hewing, 182. 

Chloride of potassium, rj^. 
Chloride of sodium, common salt, 

128, 
Chlorine as a disinfectant, 398. 
Chocolate, 452. 
Cholera, effect of hvgienic measures 

on, 372. 
Cholera, spread of, 392, 413. 
Cholesterin. a crystalline constituent 

of the bile, having a pearl-like, 

fatty appearance, 150. 
Chondrin, a nitrogenous substance, 

which may be extra cted from 

cartilage by boiling, 167. 
Chorda? tendi'nea?, fibrous m cords 

connecting the valves of the 

heart with the papillary muscles 

of the walls of the ventricles, 52. 
Chords, vocal, organ- in the larynx 

by which voice is produced, 100, 

222, 225-227. 

oid, the vascular membrane of 

the eyeball, lying between the 

sclerotic and retina, 277. 
Chyle, the milk-like fluid taken up 

by tie- lacteals from the smali in- 
line, 11, 192. 

d as it passes from 

the stomach into the small intes- 
tine, 187. 
Cilia, minute filament- attached to 

Cells, and which, daring life, are 

capable of motion. 196. 
Ciliary ligaments and muscles, 278 
Ciliated enitbelium, 3 1 1. 
Circulation affected by ei 

compared t<» ;i riv< 
conn 
" evidence of. 7<>. 

" ;md respiration, analo- 

of. 1 16. 



Circumduction, that movement of a 
limb by which it describes a coni- 
cal surface when rotating around 
an imaginary axis, 210. 

Cireumvallate, walled around, 243. 
" papilla}, 243. 

Cistern of the chyle, 44. 

Clams as food, 438. 

Clavicle, the collar-bone, 19. 

Clothing, absorption of moisture by, 
164-467. 

Clothing, for children and the aged, 
476, 477. 

Clot, the jelly-like mass formed by 
the coagulation of the blood, 83. 

Coagulation of the blood, 82, 85. 

Coccyx, the last four vertebra? of 
the spinal column consolidated 
into a siugle bone, 19. 

Coch'lea, a conical cavity of the in- 
ternal ear, 248. 

Cochlear nerve, 259. 

Complex sensations, 288. 

Cocoa, 452. 

Cod-liver oil, 460. 

Coffee, 451. 

Cold, 157. 

Cold and hp;it, feeling of, 242. 

Colon, middle portion of large intes- 
tine, 188. 

Color-blindness, inability to distin- 
guish certain colors, 268. 

Color of the blood, 130, 133. 

Colurn'nae car'neye, column-like fleshy 
elevations of the substance of the 
walls of the ventricles, 52, 54. 

Combination of actions, 20. 

Complementary colors, 267. 

Complement a 1 air, 1 12. 

Conjunctiva, the mucous membrane 

lining the eyelids and COVCrmg 

the externa] portion of the eye- 
ball, 287. 

Cones <»f the retina, 268, 27<>. 

Connective tissue, tissue made up 
of a net-work of filaments, or 

fibrous threads, and which sei'ves 

to conned the different parts of 
the body together, fibrous tissue, 
<t red lar tissue, l 7, 8 16. 

Compression of the chest, 17'>. 
u feet, 471. 

Concha, the external ear, 258. 



474 



INDEX AND GLOSSARY. 



Condiments, 449. 

Condyle, the round eminence at the 
end of a bone in a joint, 214. 

Condy's fluid, 398. 

Congestion, 68. 

Consciousness, 234. 

Consonants, 227. 

Constipation, 456. 

Constricting the neck, 470. 

Consumption, 389. 

Contraction, muscular, 18, 197,202. 
" of blood-vessels, 39, 65. 

" of the heart, 53. 

" " blood-corpuscles, 

77. 

Contraction of the bronchial tubes, 
100, 106. 

Contraction of the stomach, 184. 
cilia, 196. 

Controlling action of the nerves, 40, 
65, 69, 115. 

Convex lens, 272. 

Convolutions of the brain, 328. 

Cooking, 453. 

Cornea, the front or transparent 
portion of the wall of the eyeball, 
275. 

Cornu, a horn, 315. 

Coronary arteries and vein, 46. 

Cor'pora albican'tia, two small whit- 
ish protuberances, located in the 
angle formed by the diverging 
crura cerebri at the base of the 
brain, 327. 

Cor'pora quadrigem'ina, four hemi- 
spherical elevations lying above 
the crura cerebri, 328. 

Corpus callo'sum, a thick band of 
white nervous matter joining the 
two hemispheres of the brain, 328. 

Corpus stria'tum, the mass of nerve 
matter forming the floor of each 
of the lateral ventricles of the 
brain, 328. 

Corpuscles of bone, 350. 

" human blood, 74. 

" lymph, 92. 

" spleen, 156. 

Cortian membrane and fibres, 246, 
248, 257, 259. 

Costal, relating to the ribs, 107. 
" respiration, 110. 

Cotton as clothing, 465. 



Coughing, 111. 

Crassamentum, the thick, jelly-like 
mass formed by the coagulation 
of the blood, a clot, 83. 

Cribriform plate, a perforated plate 
of bone in the roof of the nasal 
chambers, through which the 
branches of the olfactory nerve 
pass, 244. 

Cricoid, resembling a ring, 224. 
" cartilage, 224. 

Crucial ligaments, ligaments which 
cross each other, 215. 

Crico-thyroid muscle, 224. 

Crura cer'ebri, two bundles of white 
nervous matter connecting the 
medulla oblongata with the cere- 
bral hemispheres, 328. 

Crystalline lens, a transparent doub- 
ly-convex body, situated between 
the vitreous and aqueous humors 
of the eye, 276. 

Death, local, 32. 
" general, 33. 

" modes of, 34. 
Deciduous teeth, the first or milk 

teeth, 353. 
Decussate, to cross, 333. 
Decussation of the pyramids, 333. 
Deglutition, swallowing, 182. 
Delirium tremens, 293. 
Delusive appearances, 294. 
Delusions of judgment, 292. 
" optical, 298. 
" of the senses, 292, 294. 
Dental pulp, 352. 
Dentine, the substance composing 

the great mass of a tooth, 352. 
Deodorizers, 398. 
Dermis, the under layer of the skin, 

15. 
Descending colon, 188. 
Dextrine, an amyloid substance that 

may be formed by boiling starch 

with a few drops of sulphuric 

acid, 154. 
Diaphragm, the partition between 

the chest and the abdomen, 12. 
Diaphragmata, 110. 
Diarrhoea, causes of, 411. 
Diastole, dilatation of the heart, 53. 
Diet, importance of a mixed, 173. 



INDEX AND GLOSSARY. 



475 



Digastric, two-bellied, 218, 

muscle, 218. 
Digestion, the conversion of food 

into a state lit for absorption 
into the blood, 185, 191. 

Digits, the lingers and toes, 10. 

Disease, old notions o\\ unfavorable 
to hygienic efforts, 369, 

Disease, open-air treatment of, 897. 
true idea of, 362. 
causes of, 362. 

Distillation, the process of separat- 
ing the volatile from the more 
fixed parts of a substance by 
heat, 419. 

Dorsal, pertaining to the back, 10. 
38ing the body, 408. 

Duodenum, the first portion of the 
small intestine, commencing at 
the Btomach, 188, 

Dura mater, the tough, fibrous mem- 
brane lining the cavity of the 
skull and of the spinal column, 
313. 

Duration of light-impressions, 266. 

Durham jail, 416. 

Durham and Northumberland col- 
liers, 391. 

Dysentery, 412. 

Dyspepsia, 410. 

Drinking, 183. 

Drum of the ear, the tympanum or 
middle ear, 250. 

Duet, hepatic, the tube which con- 
veys bile from the liver to the 
intestine, 1 18. 

Ductless gland-. 

Ear, 21.;. 260. 

- • in walking, 172. 

iiny of mixed diet. 1 72. 
Efferent nerves, w n es that, under 

the Btimulufi Of the central ner- 
ve:,- contractions in 
tie- musi 

Elbow-joint, 218. 

iiTiiiy h\ •_' 

; ndimentarj unborn 
you 7'.'. 

Emphysema, ;i collection of air in 
cellular sti uctures, 391. 



Enamel, the hard substance invest- 
ing the crowns of the teeth, 352. 
Endocardium, the lining membrane 

of the heart, 51. 
Endolyniph, the fluid in the semi- 
circular canals and in the vestibu- 
lar sac o\' the ear, 247. 
Entozoa, animals that live within 

other animals, parasites, 417. 
Epidermis, the outermost layer of 

the skin, 15, 341. 
Epiglottis, the lid of the glottis, 100. 
Epithelial cells, 38. 
Epithelium, the uppermost layer of 

mucous membrane, 16, 341. 
Erect position of man, 20. 
Essential food-stutfs, loo. 
Eustachian tube, a canal leading 
from the throat to each ear, 178. 
Evaporation, 169. 
Excess of food, 456. 
Excrement, the unused portions of 
the food that are discharged from 
the bowel 
Excretions, waste matter separated 
from the blood and thrown out of 
the body by the lungs, kidney-, 
skin, etc., 6. 
Excretory organs, 28. 
Exercise, 478. 

amount and time of, 491, 
" effect on circulation, 483. 
" digestion, 485. 
" respiration, 484. 
" skin, 486. 
ex( essive, 489. 
mind in, 488. 
insufficient, 490. 
11 remedial influence of, 481. 
regularity of, 192. 
Exhaustion of the retina, 267. 
Expiration, the act of expelling air 

from the lung-, 102. 
Explosive consonants 
Extension, the opposite of flexion, 

_!iten, or diaw out, 216. 
261. 
" adjustment of, 280. 

Ex .•lull, J, 

Eyelashes, ! 

Eyelids, 2;:-. 2i 

829. 



476 



INDEX AND GLOSSARY. 



Fseces, the excrement discharged 
from the bowels, 5. 

Fascia, a dense sheath of connective 
tissue enveloping bundles of mus- 
cle, 355. 

Fat, 161 
" cells, 348. 

Fauces, the cavity at the back of 
the mouth, from which the larynx 
and pharynx proceed, 178. 

Feeling, 234. 

loss of, 21. 

Femur, the thigh-bone, 20. 

Fenestra, a window, 249. 

" ovalis, and rotunda, 249. 

Fibres of Corti, 246. 

Fibrillae, very fine threads, 346. 

Fibrin, an organic compound found 
in animals and vegetables, and 
which is the part that becomes 
solid in the coagulation of the 
blood, 82, 

Fibrinogen, a substance existing in 
blood aud serous fluids, upon 
which, in connection with globu- 
lin, the property of coagulation is 
supposed to depend, 86. 

Fibro-cartilage, a substance inter- 
mediate between cartilage and 
ligament, 347. 

Fibrous tissue (see connective tissue), 
17. 

Filtration, 422. 

Fish, 436. 

Fissure of Sylvius, a large and deep 
fissure separating the anterior 
from the middle division of the 
cerebral hemispheres, 328. 

Flatulence, a collection of wind in 
the stomach and bowels, 456. 

Flesh parasites, 462. 

Flexion, the state of being bent, 216. 

Flour, 439. 

Focus, the point of convergence of 
rays of light after passing through 
a convex lens, or being reflected 
from a concave mirror, 273. 

Food-stuffs, 167. 

Form of the boot, 472. 

Foul air, effects of, on the mind, 395. 

French troops in Mexico, 411. 

Fros;, experiments with, 70. 

Fruit, 447. 



Functions, the actions of the several 
parts of a living body, 2. 

Fungiform, having the form of a 
mushroom or fungus, 243. 

Gall-bladder, the receptacle of the 
bile, 148. 

Galvanic shocks, effects of, 22. 

Game, 435. 

Ganglion, a knot of fibrous and ve- 
sicular nerve-substance, 12. 

Ganglionic cor'puscles, spheroidal 
masses of semi-solid cellular ner- 
vous matter, inclosing a nucleus 
and nucleolus, 356. 

Gaseous diffusion, 186. 

" elements in food, 167. 

Ga<es of the blood, 88. 

Gastric juice, the juice secreted by 
the stomach, upon which diges- 
tion depends, 184. 

Gelatin, a nitrogenous substance ob- 
tained from bone, ligaments, con- 
nective tissue, etc., by boiling, and 
which takes the form of a jelly 
when cold, 17, 107. 

General death, 33. 

Glands, 101. 

" buccal, 179. 

" lachrymal, 287. 

" Meibomian, 286. 

" parotid, 179. 

11 of Lieberkiihn, 161. 

" submaxillary, 179. 

" sublingual, 179. 

Glasses, concave and convex, 272. 

Globulin, an albuminous substance 
in red blood-corpuscles, 76. 

Glomerulus, a bunch of looped cap- 
illaries in the terminal dilatations 
of the renal tubuli, 137. 

Glossopharyngeal nerve, a nerve of 
the tongue and pharynx, 330. 

Glottis, the opening from the phar- 
ynx into the windpipe, 100. 

Glucose, a name applied to fruit- 
sugar, and also to that elaborated 
by the liver, 153. 

Gluten, the adhesive principle of 
grain, 167. 

Glycocholate of soda, 150. 

Glvcocholic acid, an acid of the bile, 
150. 



INDEX AND GLOSSARY. 



477 









Glycogen, a product of the liver, re- 
Bembling starch in composition, 
148. 

Goats' milk, 430. 

Goitre, or Derbyshire neck, a swill- 
ing of the thyroid gland, 155. 

Gout, :»T". 
Grassi's experin 
Gray matter, 316. 
Gullet, the oesoph'agus, 1 

Gums, the, 
Gustatory nerv< s, _ 



Haematin, the coloring-matter of the 
blood, 76. 

Ha*moglo bin, a red, semi-fluid sub- 
stance in the interior of red blood- 
eorpuscles 

Hairs, 

Hand. 214. 

Hard wal 

Haversian canals, minite canals, 
containing medullary matter, and 
occurring in the substance of bone, 

Head, 10. 

movements of, 214. 
Hearing, _ 
Heart. In 

beating ol 

I ositi : 

SOU] 

Btructu] 
rhythm ot. 

M walls of, 48. 
working ofj 

ration <»f. 157. 

M pio.li; 

u 

!. 17. 

u duct. 1 1-. 

M vein, 17. 

litary tra as 

of bodily de- 

Heredttai - won ol ins 

1 72. 
Hilns of tin- kidney, tfa • notch in 
the internal border of the ki 



where the nerves and vessels pass 
into the organ, 13 l. 

Hinge-joints, 2 18, 

Hip-joint, 213. 

Histology, an account of the minute 
structure of tissues, 339. 

Horripilation, a sensation of creep- 
in-, or as it' the hairs of the 

Human milk, 1 

Humerus, the bone of the arm, from 

shoulder to elbow, I'll. 
Humor, aqueous, the transparent 

fluid in the front part of the 

between the cornea and the 

talline lens, 276. 
Humor, vitreous, the fluid in the 

posterior chamber of the 

276. 
Hunger, 4. 

Hydrochloric acid, l s 4. 
Hydrogen, a gas. the lightest of the 

elements; one of the constituents 

of water, 168. 
Hygroscopic wal 
Hyoid bone. 2 _ ! . 

Ice-chamber experiment, o. 

Ileo-ca^cal valve, the valve at the 
openiug of the ileum into the 
caecum, L88. 

Ileum, the third divi-ion of the 
small intestine, i s ^. 

Iliac arteries, 129. 

Ilium, one of the bone= of the pel- 
vis, 19. 

Illusi 

rmperfeel joint-. 

Impu- • of, upon the 

3, 118. 

th in 

each jaw ; the cutting-teeth, 1 80. 

. "ii- of the bOD mid 

die 

Fndian-coin. I 12. 
Ingrowing toe-nails, 

Innervation, that vital prOCCSfl DJ 

which ii' ifl comma- 

o any part, 310- 
. 

with the food, l 82. 
spiration, 111. 
Inspiration and expiration, the How 



478 



INDEX AND GLOSSARY. 



of air into and out of the lungs, 
100. 

Integument, the skin, 15. 

Inter-articular cartilage, plates of 
cartilage separating the articular 
surfaces of two bones in a joint, 
211. 

Intercellular substance, substance 
lying between cells, 342. 

Intercostal muscles, 107. 

Intervertebral foramina, openings 
between the vertebrae, 314. 

Intestine, small, the duodenum, jeju- 
num, and ileum, 188. 

Intestine, large, the caecum, colon, 
and rectum, 188. 

Intralobular veinlet, 148. 

Invertebrate animals, blood-corpus- 
cle of, 79 

Iris, the delicate muscular mem- 
brane in the front chamber of 
the eye, perforated to form the 
pupil, 278. 

Ischium, a bone of the pelvis, 188. 

Jaws, 181. 

Jejunum, the middle portion of the 

small intestine, 188. 
Joints, 208-215. 
Judgments and sensations, 291. 
Jumping, 214. 

Kidneys, 134-140. 

" compared with lungs and 
skin, 147. 

Knee-pan, 19. 

Kreatin, one of the nitrogenous ex- 
tractives of muscle, 199. 

Labyrinth, bony, 246. 

" membranous, 246. 

Lachrymal duct, 287. 
gland, 287. 
" sac, 287. 

Lacteals, the vessels which take up 
and convey the chyle from the in- 
testines, 44, 188. 
Lactic acid, 184. 
Lacunae, small cavities in bone, 

350. 
Lancelot, a small fish, with very 

rudimentary organs, 79. 
Laryngoscope, an instrument for 



viewing the larynx in the living 
subject, 100. 
Larynx, the upper part of the tra- 
chea or windpipe, 100. 
Lead-poisoning, 409. 
i Lens, crystalline, one of the parts 

of the eye, 276. 
! Levator muscle of the eyelid, 286. 
| Levers of the bodv, 203. 
| Life, 31, 32. 

: Ligament, suspensory, a membra- 
nous frame which holds the crys- 
talline lens in position, 276. 
Ligamen'tum te'res, a round liga- 
ment attached to the head of the 
thigh-bone and to the bottom of 
its socket, 211. 
Ligaments, 19. 

Light and heavy clothing, 463. 
Limestone-waters, 406. 
j Limiting membrane, 263. 
Linen, 464. 
! Liver, 148. 

11 cells, 149. 
" sugar, 154. 
! Lobes of brain, 327. 
Lobules of liver, 148, 150. 
Local death, 32. 
Locomotion, 194, 216. 
Long-sight, 284. 
Loose clothing, 417. 
Lungs, 99. 

" amount of work done by, 104. 
" their arteries and veins, 45. 
u kidnevs and skin compared, 
147. 
Lymph, the colorless transparent 
fluid in the lymphatic vessels, 92. 
" corpuscles, 79. 
Lymphatic capillaries, 43. 
" glands, 43. 

" system, 43. 

Macula lutea, a yellowish spot on 

the retina, 262.' 
Magnifying-glasses, 303. 
Malarious fevers, 415. 
Malleus, one of the bones of the 

middle ear, 251. 
Malpighian capsules, dilatations at 

the outer extremities of the renal 

tubules, 137. 
Mammals, blood-corpuscles of, 79. 



INDEX AND GLOSSARY. 



479 



Marrow, the fatty substance in the 

cavities of long bones, 350. 
Marsh-water, i 
Mastication, chewing, 182. 
Moat-, 433. 

Medical management, 609. 
Medulla marrow. 2 >2. 

Oblongata, a continuation 

of the spinal marrow within the 

cavity of the skull, 1 15. 
Membrane, arachnoid, 312. 

of Corti, 246. 
Mental emotion, 69. 
Mes enteric glands, lymphatic glands 

of the mescntcrv, 44. 
Mes entery, the membrane which 

suspends the -mail intestine to 

the back wall of the abdomen, 

1 1. 
Metacarpus, metacarpal bones, five 

cylindrical hone- situated be- 

tween the wrist and the fingers, 

211. 
Milk, 430. 

u teeth. 353. 
Mind, controlling power of, 22. 

in exercise, 188. 
Mineral aliments, 428. 

ingredients of water, 406. 
Mitral valve, the valve between the 

left auricle and ventricle, 52. 
Modiolus, the central pillar of the 

cochlea of the ear, 248. 
Modulation of tie' voice, 229. 
Molar-, the grinding4eeth, 354, 
Motion and Locomotion, 194-231. 
Motor nerves (set efferent nerves), 

Moton - oculi, the nerves distrib- 
uted to the mUSCl - that move 

tie- eyeball, 329. 
Mouth, 25, US. 

is membrane, the lining of the 
Cavities of the body which com- 
municate with the exterior, l*">. 

is, tie- fluid secreted by mucous 
membranes, 16. 
SI i, 18, 168, 197, I 

" of the eyeball, 

" of the heart, 51. 
" of the mouth, 181. 

" striated and -mooth. '■ 



Muscle, 191 

Muscular contraction, 198. 

Muscular sense, the sensation of re- 
sistance experienced when bodily 
movement is impeded, 236. 

Musical notes, 22T. 

Mustard, 449. 

My'osin, the coagulable constituent 
of muscle, 199, 

Nails, 342. 

Nares, the nasal cavities, 115, 211. 
Nasal passages, 244. 
Nerve-fibres, 356, 358, 367. 

Nerves, action of, on blood-vessels, 

160. 
Nerves, action of, on glands, 161. 
" action of, on the kidneys, 
139. 
Nerves, action of, on muscles, 197- 

199. 
Nerves, action of, on respiration, 115. 
l< action of, on the stomach, 
184. 
Nerves, action of, on the sweat- 
glands, 145. 
Nerves, auditory, 246, 248, 251, 258, 

330. 
Nerves, facial, 330. 

" glosso-pharyngeal, 329. 
" gustatory, 329. 
" motor or efferent, and sen- 
sory or afferent, 232, 311), 320. 
Nerves, olfactory, :i2'.i 
" ol' the brain, 330. 
" of the eve, 261, 263, 330. 
" of the tongue, 330. 

" of tie- heart. 69. 

Nervous action, rapidity of, 366. 

system and innervation, 30, 
3K>- 

Nervous tissue, 356-359. 

Neurilemma, the delicate fibrous 
sheath covering the nerves, 356. 

Nitrogen, element ; one 

of the chief constituents of the 
air, and of all albuminous com- 
pounds, 1, I"-, L68, 167, 360, 

Nitrogen, starvation, 1 7'». 

Norwood School, 890, 
244. 

Nuclei and nucleoli, 78, :; i»;. 

Nutrition, the assimilation of nutri 



480 



INDEX AND GLOSSARY. 



tive matter, 24, 164-193, 351, 
355, 356, 359. 

Odontoid process, a tooth-shaped 
peg on the axis vertebra, 214. 

(Esoph'agus, the gullet, a muscular 
tube extending from the pharynx 
to the stomach, 100. 

Olecranon, a projection of the ulna 
at the elbow, which prevents the 
forearm being bent backward on 
the arm, 213. 

Olfactory nerves, 329. 

Optic axis, 299. 

" nerve, 261, 263, 264, 270, 
275, 285, 330. 

Optic thalami, two great masses of 
nervous matter into which the 
crura cerebri pass, 115. 

Optical delusions, 293. 

Orbicularis muscle, a circular mus- 
cle which shuts the eye, 286. 

Os orbicula're, one of the small 
bones of the middle ear, 251. 

Osmo'sis, the intermixture of liquids 
which takes place through a moist 
membrane, 186. 

Ossicles, auditory, the small bones 
of the middle ear, 251. 

Ossification, 351. 

Otoco'nia or otolithes, minute par- 
ticles of calcareous matter in the 
membranous labyrinth of the ear, 
246. 

Oxygen, one of the gaseous ele- 
ments, a large constituent of wa- 
ter and air, and the great sup- 
porter of combustion and respi- 
ration, 3, 29, 35, 99, 103, 104, 
123, 125, 152, 165, 360, 375, 377, 
378, 381, 389. 

Oysters, 438. 

Palate, hard and soft : the former is 
the bony roof of the mouth ; the 
latter a fleshy membrane attached 
to the former, and hanging be- 
tween the mouth and the phar- 
ynx, 178. 

Pallor, 66. 

Palpitation, 69. 

Pancreas, a large gland which pours 



its secretion into the duodenum; 

the sweet-bread, 12. 
Pancreatic juice, the fluid secreted 

by the pancreas, 191. 
Pancreatic duct, 184. 
Papillary muscles, muscular eleva- 
tions of the walls of the ventricles 

of the heart, 52, 54. 
Papilla?, conical elevations of the 

deep layer of the integument, 239. 
Papillae, filiform, elongated papillae 

tapering to a point, 243. 
Papillae, fungiform, papillae that are 

broad at the top and narrow at 

the base, 243. 
Par vagura, the pneumogastric 

nerves, 330. 
Paralysis, 319. 
Parke's experiments, 397. 
Parot'id gland, a salivary gland situ- 
ated under the ear, 179. 
Parsnips, 446. 
Patella, the knee-pan, 19. 
Peas and beans, 445. 
Pelvis, the bony girdle at the base 

of the trunk, 19. 
Pelvis of the kidney, 137. 
Pepsin, one of the constituents of 

the gastric juice, 184. 
Peptic glands, glands in the mucous 

coat of the stomach which secrete 

the gastric juice, 184. 
Peptone, a solution of proteid mat- 
ter effected by the gastric juice, 

186. 
Pericardium, the membranous bag 

which incloses the heart, 48. 
Perilymph, the watery fluid in the 

canals of the ear, 247, 251, 257. 
Periosteum, the thin membrane 

forming the immediate covering 

of the bones, 350, 351. 
Peristaltic contraction, applied to 

the contraction of the muscular 

coat of the intestine, 190, 201. 
Peritonae'um, a membrane which 

coats all the walls and viscera of 

the abdomen, 148, 188. 
Perspiration, 141-146, 364. 
Petrosal Done, so named from its 

hardness, 246. 
Phalan'ges, the joints of the fingers 

and toes, 10. 



INDEX AND GLOSSARY. 



4-1 



Pharynx, the cavity into which the 
mouth, nose, upper end o\' the 
alimentary canal, and the wind- 
pipe open. 

Phosphate of lime, 19. 

Phosphenes, luminous appear 

ised by pressing the eyeball, 

systematic account of 

the actions of firing 
Pia mater, the : rnal of the 

three membranes of the brain, 

_ tent-cells, cells containing the 
stance which gives color t«» a 

part. ." 
Pilhrs of the diaphragm. 1">. 
riv..t-joint, 214. 
Plasma, the nearly colorless fluid of 

the bloo ■':. 
Pleura, a serous membrane lining 

the cavity of the thorax and in- 

Pneumogastrie nerves, the tenth 
pair distributed to the larynx, 

luniks, liver, and stoma/ 

nee connecting the cerebrum, 

cerebellum, and the medulla ob- 

Portal circulation, the flow of the 
blood fr< lominal fh 

the liver to the h< | 
vciii. 

Portio dura and portio moDifl 
har d the 

Potter's asthma, 

T i«.n. tli.- act of turnii _ 
palm of the hand d< 

Prot. 

1 7", 

Ptyahn, 

eilli.ii odOl . : 
Pul; 



Pulmonary consumption, : 

capillaries, 9&-101. 

vein, 46. 
Pulse. 
Puncta lachryma le. two small ori- 

fioes in the edges of tl 

near the inner corner of the 

Puritieati. I 

of a 
Purkinje's figures, -7". 

a 
Pylorus, the opening from the Btom- 
ach into the duodenum. 184. 

Radial fibres, 203. 
Racemose glands, clustered l; 
161. 

Radius, one of the bones of the 

forearm, 214. 
Rain-watei . 

hyle, 44. 
im, the third and lowest pait 
of the 1 • . I B8. 

Reflei action. 116, i 

artificial, 
Regulation of temperature. 
Renal, relating to the kidm ys, 187. 
■ s, 187. 
circulation^ 188. 
excretion ! 
Lual air, 112. 

3 
affected bv 
hi. 

and circulation com- 
pared, 1 16. 

•i, different in the two 
111. 

■ f, en circula- 
tion. 11'.'. 
Respiration, n 

I 1 B, 
Halpighii (Malpigbi'fl net- 
irork i, a mucous - 

the 
841. 

lUCO -mn, 841. 

►n <>t the optic 
i e u ithin 1 1 * • - ball of tl. 
261, - 

the heart, 



482 



INDEX AND GLOSSARY. 



Ribs, 105. 
Rice, 444. 
Rickets, a disease of the bones in 

childhood, 457. 
Rigor mortis, death-stiffening, 198. 
River-water, 406. 
Roasting, 454, 

Rods and cones of the retina, 263. 
Rotation, the act of turning round, 

216. 
Running, 221. 
Rye, 440. 

Sacrum, one of the bones in the 
spinal column, consisting of the 
twenty - sixth, twenty - seventh, 
twenty-eighth, and twenty-ninth 
vertebras, 19. 

Salamanders, blood corpuscles of, 79. 

Sand-and-gravel waters, 406. 

Sanitary congress, 407. 

Saliva, the juices of the mouth, 179, 
182. 

Salivary glands, 179. 

Sarcolemma, the sheath investing 
the elementary fibres of muscle, 
51, 355. 

Scala, a stair, 248. 

Scala media, vestibuli, and tym- 
pani, 248. 

Scapula, the shoulder-blade, 19. 

Scarf-skin, the same as epidermis, 
15. 

Sclerotic, the outer coat of the eye- 
ball, 275. 

Scrofula, 390. 

Scurvy, 372. 

Sea-water, 406. 

Sebaceous glands, glands in the 
skin, secreting an oily matter, 
142. 

Secretory glands, 132. 

Semicircular canals of the ear, 249. 

Semilunar valves, valves at the junc- 
tion of the aorta and the left 
ventricle, and of the pulmonary 
artery and the right ventricle, 52. 

Sensation, 287. 

Sensations and judgments, 290. 
" coalescence of, 288. 

" and sensory organs, 23, 

232. 

Senses, delusions of, 292. 



Sensory nerves, 232. 
" organs, 23. 
Septum, a partition, 245. 
Serous membranes, 48. 
Serum, a clear, yellowish liquid 

found in the blood, and also con. 

tained in the peritonaeum, pericar* 

dium, and other serous mem' 

branes, 83. 
Sewage gases, 413. 
Shallow wells, 406. 
Short-sight, 284. 
Shoulder-joint, 212. 
Sick-room atmosphere, 394. 
Sighing, 111. 
Sight, 237. 

" organ of, 261-288. 
Simple sensations, 289. 
Singing, 227. 

Skeleton, number of bones in, 19. 
Skin, 15, 28, 141-148. 

11 lungs, and kidneys compared, 

147. 
Skull, the brain case, 10, 11, 19. 
Smell, 244, 245. 

11 loss of, 245. 
Smooth muscle, 355. 
Sneezing, a convulsive action of the 

respiratory muscles, 245. 
Sniffing, 245. 
Soft palate, 178 
" water, 405. 
Sound, 254. 

Speaking-machine, 231. 
Speech, 228. 
Sphincter, a ring-like muscle closing 

an aperture, 134. 
Spinal accessory nerves, 331. 

" canal, 12. 

" column, bones of, 19. 

" cord, 314-325. 

" " conducting power of, 325. 
Spinal cord, injuries to, 21. 

" nerves, 314. 
Spleen, a large, deep-red viscus on 

the left side of the stomach, in 

the abdominal cavity, 156. 
Splenic artery, the artery supplying 

the spleen, 156. 
Splenic vein, 156. 
Squinting, an affection of the eye in 

which objects are seen in an ob- 
lique manner, 307. 



INDEX AND GLOSSARY. 



483 



Stapedius, a muscle of the tympanum 

of the ear, 252. 
SU pes, a stirrup-shaped ossiele of 

the ear, 261. 
Starch, 167, 439. 

Stationary air, 1 13. 

Stereoscope, 309. 

Sternum, the breast-bone, 19. 

Stewing, 454. 

Stomach, 184. 

St rue, stripes, 355. 

Striated, striped, 855. 

Subjective sensations, 293. 

Sublingual glands (ae< glands). 

Submaxillary glands kk 

Subsoil water, 406. 

Sugar, 107, 4 -JO. 

Sulci, grooves on the surface of the 

brain, 328. 
Sulphate of lime, 406. 
Sulphur, 167. 

waters, 406. 
Sulphuretted hydrogen, 126, 385. 
Supination, the act of turning the 

palm of the hand upwards, 214. 
Supplemental air, 1 12. 
Supra-renal capsules, 155. 
Surface-water, 406. 

nsory ligament (see ligament). 
Sutures, union of flat bones by their 

margins, 351. 
Swallowing, 182. 
Sweat-glands, the lower extremity 

of the sweat-tubes coiled up into 

a knot, 143. 
et-bread (set pancreas). 
Symmetry of the body, 1<». 
Sympathetic system, the double row 

of nervous ganglia along the back- 
bone, l 2. 
Synovia, a lubricating fluid se< reted 

at point- of articulation, i9. 

Synovial membrane, 19 

Syntonin, the chief constituent of 
muscle, closely resembling albu- 
men in composition, 1 »*»7. 

ole, tli- contraction of the 

tile corpus- 57. 

Tannic & 

348 



Taurocholic acid, one of the con- 
stituents of the bile, 150. 

Tea, 450. 

making of, 451. 

adulteration of, 451. 
Tears, 287. 
Teeth, 180, 352-354. 
cement of, 352. 
crown of, 352. 
ilen tine of, 353. 
development of, 854. 

" enamel of, 352. 

" fangs of, 352. 

pulp-cavity of, 352. 
Temperature of the blood, 158. 
Tendons, white fibrous cords con- 
necting muscles with bone, B46. 
Tensor tympani, a muscle of the 

tympanum of the ear, 252. 
Thein, the bitter principle of tea. 

450. 
Theobromin, the bitter principle of 

cocoa, 450. 
Thickness of the blood, 87. 
Thirst, 4. 
Thoracic duct, a large tube in front 

of the backbone into which most 

of the smaller lymphatic trunks 

pour their contents, 43. 
Thorax, the chest; the cavity com 

taming the heart and lungs, 

10. 
Thought, 231. 
Thymus gland, 155. 
Thyroid cartilage, the largest of the 

cartilages of the larynx forming 

the prominence in front of the 

throat, 224. 
" gland, 155. 
Thyro arytenoid muscles, 224. 
Tibia, the shin-bone, 206* 
Tidal air, 112. 
Tight bootfl and BhOOS, 172. 

" clothing, 471. 
Tissue, 17. 

formers, 1 7'». 

Tongue. 213. 

Tongueless speech, 231. 

Tonsils, oral glands between the 

pillars of the fauces, 1 77. 
Touch, 239-242. 
Tra'chea, the n indpipe, 100 
Transfusion of blood, 91, 



484 



INDEX AND GLOSSARY. 



Transverse colon, 188. 

Trapezium, 213. 

Triceps muscle, the extensor of the 

forearm, 217. 
Trichi'na spiralis, 462. 
Tricuspid valve, the valve between 

the auricle and ventricle of the 

right heart, 52. 
Trigeminal nerve, 330. 
Tripod of life, brain, lungs, and 

heart, 34. 
Trunk, 10. 
Tu'buli uriniferi, small tubes in the 

kidney, 137. 
Tubercular consumption, 390. 
Tuning fork, 246. . 
Turbinal bones, top-shaped bones 

of the nostrils, 244. 
Tympanum, the drum of the ear, 

250. 
Tympanic muscles, function of, 260. 

Ulna, the large bone of the fore- 
arm, 214. 

Unwholesome food, 461. 

U'rea, one of the constituents of 
urine, composed of two equiva- 
lents each of oxygen, nitrogen, 
and carbon, and lour of hydro- 
gen, 135. 

Ure'ters, tubes leading from the 
kidneys to the bladder, 134. 

Ure'thra, the canal leading from the 
bladder outwards, 134. 

Uric acid, 135. 

Urine, 135. 

Utric'ulus, a minute cell or vesicle, 
247. 

Uvula, a prolongation of the soft 
palate, 178. 

Val'vulae conniven'tes, transverse 
folds of the mucous membrane 
lining the small intestine, 189. 

Valve, ileo-caecal, 188. 

Valves of heart, 52. 

u of lymphatics, 42. 
" of veins, 43. 

Vascular system, 36-54. 

Vaso-motor nerves, those which 
control the circulatory vessels, 
65, 327. 

Vegetable foods, 170-173, 439. 



| Veins, 41. 

I Velum or soft palate, 178. 
Vena cava, inferior and superior, 

45. 
Venous pulse, 121. 
Ventilation, 397. 

" effects of, on sick, 398. 

Ventral, belonging to the abdomen 

or belly, 10. 
Ventricles of heart, 49. 

" of larynx, cavities above 

the vocal ligaments, 224. 
Ventricles of the brain, 327. 
Ventriloquism, 297. 
Vermiform appendix, a worm-shaped 

process of the caecum, 188. 
Vertebra?, the bones of the spinal 

column, 11. 
Vertebrate animals, those having 

backbones, 79. 
Vestibule, 249. 
Vestibular sac, 247. 
Vibrations of ether, 264. 
Villi, minute, thread-like processes 

of the mucous membrane lining 

the small intestine, 44. 
Vinegar, 449. 
Vis'cera, the entrails ; the contents 

of the abdomen, 186. 
Vision, 305. 
Visual images, 307. 
Visual size and form, 306. 
Viscus, any large organ contained 

in any of the cavities of the body, 

as lungs, liver, spleen, 
Vital actions, 31. 

" eddy, 194. 

" food-stufifs, 167. 
Vitreous humor, the contents of the 

posterior chamber of the eyeball, 

278 
Vocal chords, 223. 
Voice, 226. 
Volition, 234. 
Vowels, 228. 

Walking, 220. 

Warmth, 242. 

Waste-pipes, 408. 

Water, amount daily taken, 402. 

" camera, 275. 

" poisoning, by lead, 409. 

" purity of, 407. 



INDEX AND GLOSSARY. 



485 



Wheat, 439. 
Whispering, 228. 
Whistling, 228. 

White clothes, 467. 
White matter of brain, 316. 
Windpipe, the trachea, 100. 
Wisdom-teeth, 364. 
Woolen, 466. 



Work and waste, < 
Wrist, 214. 

Yellow spot, 262. 

Zein, 442. 
Zootropc, 306. 



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academies, edited from Ganot's Popular Physics by William G. Peck. 

Quackenbos's Natural Philosophy $1.22. 

Designed to exhibit the application of scientific principles in every-day life. 

Steele's Popular Physics $1.00. 

Designed both to interest and instruct the pupil. Written in simple language, and 
containing many practical illustrations. 

Trowbridge's New Physics. ....... $1.20. 

A manual of experimental study for high schools and preparatory schools. 

Wells's Natural Philosophy $1.15. 

This embodies the latest and best results of scientific discovery and research. 

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[*6 9 ] 



MAR 2 8 1949 




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